1. Introduction

Northeast Asia is an important geographical unit located in the northeastern part of Asia. Geographically, it mainly includes northeastern China, eastern Inner Mongolia, Japan, North Korea, South Korea, Mongolia, and the Far East region of Russia. It is rich in natural resources, has an important geographical location, a unique and diverse culture, and a complex and challenging political situation. As a result, it plays an important strategic role in the global economic and political landscape and is of great significance to world peace and development. The Northeast Asia region is home to a number of globally leading political, economic, and military powers, with China, Russia, and Japan as the main representatives. In this situation, the major powers are roughly balanced, maintaining regional stability.

The power balance is an important concept in the field of international relations, primarily referring to a state of relative equilibrium in the balance of power among nations or groups of nations within the international system. In such a state, no single nation or group of nations can achieve absolute dominance, thereby preventing a major power from exerting overwhelming control over others. This maintains relative stability within the international system and plays a significant role in preserving peace and stability.

In the 1920s, Northeast Asia enjoyed a period of relative stability and peace. Research has shown that, unlike other regions of China during the same period, which were plagued by frequent revolutions and civil wars—especially the massive revolution that swept across most of China—the Northeast Asia region in the 1920s exhibited an unusually peaceful state. From the beginning of this period until the Huanggutun Incident and the the Chinese Eastern Railway Incident, over nearly a decade, the only exception was the rebellion led by Songling Guo (which lasted only one month and its impact was limited to parts of present-day Liaoning Province), there were no armed conflicts, confrontations, or interventions by Japan, Russia, or other major powers on the Northeast Asian mainland, nor were there any domestic wars. The region remained generally peaceful and stable, with some development in industries such as manufacturing. The reasons behind this were multifaceted. First, the strength, strategies, and mutual constraints of regional major powers such as Japan and Russia played a role. Second, international treaties and systems exerted relative constraints. Third, the growing strength and foreign policies of local powers in Northeast China contributed to the stability. Fourth, the policies and interventions of Western powers outside the region also had an impact. It was the power struggle among China, Japan, the Soviet Union, and Western powers that created a relatively stable situation, i.e., the existence of a relative power balance. Studying this issue and analyzing the complex political, economic, and military interactions in Northeast Asia during this period can further reveal the dynamic mechanisms related to the power balance, supplement the traditional power balance theory's insufficient explanation of non-military balancing factors, enrich the international political theory system, and also provide historical insights for the current situation in Northeast Asia.

2. Literature review

The theory of power balance has a long history, originating in Europe and developing extensively there. In terms of the construction of international systems and international order related to the power balance, Guoshun Yang explains that the Vienna System established a typical modern power balance system, arguing that this was a great power balance of power regime dominated by the five major powers in Europe, and that it was a relatively more stable power balance system compared to the Westphalian System [1]. Shian Li also noted this system that sought balance and aimed for a roughly equal distribution of power among the major powers [2]. Zhaogen Chu analyzes the issue from the perspective of ideas and concepts, arguing that after the establishment of the Vienna System, the maintenance of the status quo in Europe and the pursuit of power balance became the dominant guiding principles of European great powers' foreign policies. However, the great powers differed in their approaches, methods, and means of addressing conflicting interests, primarily dividing into conservative and liberalist factions [3].

In terms of the power balance diplomacy and policies of European countries in modern times, Zijuan Wang compares the characteristics, causes, similarities, and differences between the British power balance model and German during the Bismarck era, as well as their roles in specific periods. It concludes that the Bismarckian power balance model is a more worthwhile model to draw upon [4]. Shufang Zhao also mentions that one of the key factors enabling Russia to rapidly emerge as a European power in a short period of time was its frequent and skillful use of power balance diplomacy [5].

In terms of the Northeast Asian landscape and international relations, Lisha Cheng, Shijun Wang, and Ran Yang provides an in-depth analysis of the evolution of geopolitical relations in the Northeast region since the 20th century, focusing on the geopolitical landscape and stakeholders in the Northeast during the 1910s to 1940s, and finally proposing strategic measures for the development of geopolitical relations [6]. Shengfa Zhang addresses the Chinese Eastern Railway issue, discussing the great powers' competition over it, the rivalry among various forces in Northeast China [7]. Naihe Zhang examines the situation in Northeast Asia from a historical perspective, focusing on the institutional framework, dominant forces, and external influences in the region [8].

Overall, research findings on the power balance or the modern Northeast Asian landscape cover a wide range of fields and are in-depth, laying a solid foundation for subsequent research.

However, previous studies also have some shortcomings. In terms of research focus, most scholars have focused on the turbulent and chaotic periods in Northeast Asia and explored its international relations and regional landscape, but few have paid attention to the relatively stable 1920s in Northeast Asia and conducted in-depth studies on its internal and external causes. Additionally, few scholars have introduced the power balance theory into historical research on East Asia and Northeast Asia. Therefore, there are certain academic gaps in the aforementioned areas. Based on this, this study primarily focuses on the relatively peaceful and stable 1920s in Northeast Asia's modern history, describing the specific manifestations of the characteristics of that era, and introducing the power balance theory from the field of international relations. It analyzes the multiple factors influencing the relative stability of Northeast Asia in the 1920s from different perspectives, providing new insights and methods for future research.

3. The formation of the idea of power balance and its application in Europe

3.1. The Vienna system and the principle of power balance

At the end of the 18th century and the beginning of the 19th century, during the later stages of the French Revolution, Napoleon launched a series of foreign wars, using warfare to export the revolution to Europe. The radical ideas of the French Revolution shattered the traditional feudal order, while the wars plunged the European continent into turmoil, shattering the old international order. In this context, Britain, which had already entered the capitalist stage, and the feudal monarchies of Europe formed an anti-French alliance, ultimately defeating the Napoleonic Empire. Following the signing of the First Treaty of Paris in 1814, the monarchs and representatives of the victorious nations arrived in Vienna, the capital of Austria, to convene the Congress of Vienna. The congress aimed to establish a new international order in Europe based on the new balance of power. Following Napoleon's return to Paris, the monarchs and ministers of the various nations in Vienna simultaneously organized the Seventh Coalition against France to confront Napoleon militarily while hastily adopting the Final Act of the Congress of Vienna, thereby concluding the Congress. This Final Protocol, along with the Second Treaty of Paris and other treaties signed by the relevant nations after Napoleon's complete defeat, ultimately formed what is known as the Vienna System.

As contained in the specific treaties included in the Second Treaty of Paris: The Final Treaty between Great Britain, Austria, Prussia, Russia, and France; The Special Treaty between Great Britain, Austria, Prussia, Russia, and France Regarding France's Payment of Indemnities to the Allied Powers and the Special Treaty Between Great Britain, Austria, Prussia, and Russia and France Regarding the Military Occupation Lines of the Allied Forces in France [9], the major powers collectively dominated the international order of the time. Here, the principle of power balance is examined from the perspective of international relations, meaning that the power balance principle in the Vienna system has become a fundamental form of international order.

The principle of power balance in the Vienna System aimed to maintain the power balance among the European great powers, preventing any single country from dominating and monopolizing the European continent. It achieved this by establishing a balanced power structure to prevent France from rising again and dominating Europe, while also preventing other countries from over-expanding. This allowed the European great powers to mutually constrain one another in a relatively balanced state, thereby maintaining Europe's political order. In this state, “the distribution of power among great powers is extremely unequal, but this does not necessarily mean that the most powerful nation holds a dominant position, as other nations may unite to counterbalance it” [10]. In this sense, the mutual checks and balances of power and the sustained state of peace and stability are achieved. This 19th-century European power balance system aimed to prevent violent conflicts and protect the independence and security of nations, but its implementation required active maintenance by member states and the formation of alliances to counter potential aggressors [11]. Therefore, in practical implementation, through the redistribution of territories to achieve relative balance among nations, the establishment of buffer states like Switzerland as a permanent neutral nation to mitigate direct military conflicts between great powers, and the formation of a structure dominated by the five great powers along with a diplomatic mechanism of European Coordination to resolve disputes, the principle of power balance was successfully upheld, maintaining power equilibrium and stability.

3.2. The practice of power balance diplomacy representing the state

3.2.1. Britain's power balance diplomatic strategy

Former British Prime Minister Winston Churchill once wrote in his memoirs of World War II: “For 400 years, British foreign policy has been opposed to the emergence of the most powerful, aggressive, and domineering nation on the continent, particularly preventing the Low Countries from falling into the hands of such a nation” [12]. This serves as the most appropriate and apt description of Britain's power balance foreign policy.

During the Victorian era following Palmerston's appointment as Foreign Secretary, Britain's power balance diplomacy was clearly evident. “On the Eastern Question, to curb Russian expansion, Britain on one hand entered into a collective assistance agreement with Russia, Austria, and Prussia to support Turkey against Egypt, thereby preserving Turkey as a buffer state against Russia; on the other hand, it allied with France to provoke the Crimean War, halting Russian expansion in the Balkans, maintaining the European power balance, and eliminating the threat Russia posed to British naval power in the Mediterranean” [4].

3.2.2. France's power balance diplomacy and equilibrium

Due to the depletion of France's national strength by the Napoleonic Wars and the pressure of post-war reparations, France's power was weakened. In this situation, France implemented a power balance diplomacy policy, striving to reestablish its status. France was well aware of its limited capabilities and the difficulty of directly challenging other major powers, so it employed clever tactics to navigate the complex relationships among the European great powers. Its core strategy was to prevent any single nation from gaining too much dominance and to maintain a relative balance of power among all nations.

In practice, France actively participated in the coordination of European affairs, demonstrating its status as a major power. In the Greek independence issue, France joined forces with Britain and Russia to oppose the Ottoman Empire, thereby striking a blow to Ottoman power in the Balkans, preventing Russia from dominating the region, and enhancing France's influence in Europe. Additionally, France exploited the contradictions between other major powers. During the struggle between Prussia and Austria for leadership in Germany, France initially adopted a wait-and-see attitude. Once the contradictions between the two sides intensified, France intervened at the appropriate time to balance the powers of Prussia and Austria, ensuring that no unified and powerful state emerged in the German region that could threaten its own security.

Under the guidance of this foreign policy, through a policy of power balance diplomacy and practice, France gradually recovered its strength under the Vienna System, regained the respect and influence of the major European powers, and maintained the balance of power on the European continent for a certain period of time, thereby avoiding the outbreak of large-scale wars.

3.2.3. Russia's power balance foreign policy and expansion

The concept of power balance is rarely mentioned openly in Russian diplomacy. In this sense, to a certain extent, it is more of a diplomatic technique than a diplomatic ideology for Russia.

In the long run, Russia's economic and political power is inferior to that of the major powers in Western Europe. “One of the key factors enabling Russia to rapidly emerge as a European power in a relatively short period of time was its frequent and skillful use of power balance diplomacy. By fully exploiting the contradictions among the great powers and the mutual checks and balances between multiple strong nations, Russia sought to divide the great powers, either to reverse unfavorable circumstances or to leverage the diversity of forces to assert its own influence. This approach almost became a tried-and-true diplomatic art form for Russia.” Additionally, "Facing weaker nations in the East, during the Tsarist era, Russia simultaneously competed with European great powers to secure interests in Europe while expanding its territories eastward, conquering vast regions such as Siberia, the Caucasus, and Central Asia through military force, promoting hegemony and power politics, and consolidating its expansionist gains through unequal treaties” [5]. Through a combination of power balance diplomacy and military expansion, Russia's strength and status significantly increased, propelling it into the ranks of European great powers.

4. The Northeast Asian landscape in the 1920s under the power balance and other factors

4.1. Northeast Asia in the 1920s

From a national perspective, the early 20th century was a turbulent period marked by political instability, the intertwining of various factions, and tense international relations. Setting aside the situation during the late Qing dynasty at the turn of the 20th century, China in the 1910s—following the Xinhai Revolution, the establishment of the Republic of China, and the abdication of the Qing emperor—was immediately plunged into a series of events including the Second Revolution, the Protection of the Nation Movement, the Protection of the Constitution Movement, the New Culture Movement, the May Fourth Movement, and China’s participation in World War I. In the 1920s, a series of political changes occurred, including the founding of the Communist Party of China, the independence of Outer Mongolia, the first cooperation between the Kuomintang and the Communist Party, the National Revolution and the Northern Expedition, the breakdown of the Kuomintang-Communist alliance, the change of flags in Northeast China, the China-Soviet Railway Incident, and multiple warlord conflicts. By the 1930s, the Central Plains War, the September 18 Incident, and the establishment of the puppet state of Manchukuo further exacerbated the unstable and turbulent situation. It can be seen that during the three decades of the early 20th century, from a national perspective, China's domestic situation was extremely unstable, with frequent changes in government, factional struggles, and wars. Internationally, major powers were watching closely, and although the situation was relatively calm during World War I, there were still ambitions and encroachments from countries like Japan.

Narrowing our focus to Northeast Asia, over the past three decades, we have witnessed the 1900 Hailanpao Bloodshed and the Jiangdong 64 Villages Massacre perpetrated by the Russian Empire, followed by its occupation of Chinese territory. This was followed by the Russo-Japanese War, the signing of the Sino-Japanese Joint Military Agreement Against Enemies, Japan's deployment of troops to Siberia, the Sino-Soviet Agreement on the Settlement of Pending Issues, the Huanggutun Incident, the change of flags in Northeast China, the Chinese Eastern Railway Incident, the September 18 Incident, and the establishment of the puppet state of Manchukuo. From this series of political changes and international events, it is evident that Northeast Asia was far from peaceful during this period.

However, upon closer examination, an unusual phenomenon can be observed: compared to the chaos prevailing across China during the same period and the overall turmoil in Northeast Asia during the 1930s, the Northeast Asian region in the 1920s exhibited an unusually stable situation, particularly within China. This stability persisted except for the 1922 withdrawal of Japanese troops from Siberia (by the 1920s, Japan's military presence in Siberia was no longer at its most tense), the Huanggutun Incident and the change of flags in Northeast China in 1928, and the Chinese Eastern Railway Incident in 1929, Northeast Asia maintained a continuous period of peace, tranquility, and relative stability lasting six or seven years. During this period, China signed the Sino-Soviet Agreement on the Settlement of Pending Issues with the Soviet government in 1924, marking the first equal treaty China had concluded with Russia since the Opium War. This can be regarded as a diplomatic victory for modern China. Thus, the relative stability and peace in Northeast Asia during the 1920s were highly unusual and rare.

4.2. The role of traditional power balance factors

4.2.1. The strength, strategy, and mutual constraints of major regional powers

In 1917, the October Revolution erupted in the Soviet Union (USSR). Under the leadership of Lenin and others, the Russian working class launched an armed uprising, overthrew the provisional government, and established the Soviet Union. In 1922, the Soviet Union was officially established. During the 1920s, the Soviet Union successively implemented the New Economic Policy, “socialist industrialization,” “agricultural collectivization,” and the restoration of the national insurance system, and developed its industrial economy through the “Five-Year Plans.” Additionally, under the gradually established planned economic system, the Soviet Union concentrated its efforts on developing heavy industry. With the strong promotion of the state, the economic and social strength of the Soviet Union (Union of Soviet Socialist Republics) was significantly restored and developed, with its overall strength markedly enhanced compared to the post-revolutionary period. Its growing strength also made the Soviet Union a powerful and unignorable force in Northeast Asia, profoundly influencing and shaping the regional situation in the region. This was particularly concerning to Japan, which had been forced to withdraw its troops from Siberia in 1922.

In its policies toward China and Japan, the Soviet Union also adopted a more self-serving strategy, signing the Sino-Soviet Agreement and the Soviet-Japanese Agreement with China and Japan respectively, establishing diplomatic relations with both countries, and seeking to replace the old Russian interests in the Chinese Eastern Railway. Meanwhile, through the Japan-Soviet Agreement, it brought an end to Japan's anti-Soviet armed intervention following the October Revolution and temporarily thwarted Japan's attempt to exploit the Soviet Union's domestic civil war and temporary diplomatic difficulties to occupy the Soviet Union's Far Eastern regions.

In Japan, following the Meiji Restoration, the country embarked on a capitalist path, strengthening its national power and rapidly rising to prominence. After the First Sino-Japanese War, Japan obtained massive war reparations and extensive territorial concessions from the Qing government, further enhancing its strength. In the early 20th century, Japan achieved victory in the Russo-Japanese War, defeating the Russian Empire. Through the Treaty of Portsmouth, Japan acquired a series of political and economic rights, including the Lushun and Dalian concessions, the Chinese Eastern Railway branch line, and other associated interests that Russia had previously seized from China. This further expanded Japan's influence, even surpassing Russia's presence in Northeast Asia, transforming the situation in Northeast China from being dominated by a single country to being divided between two nations, one in the north and one in the south. By the 1920s, although Japan had failed to achieve its goal of occupying Russia's Far East territories, it still possessed formidable national strength and maintained a pivotal presence in Northeast Asia.

Japan has consistently prioritized Northeast Asia, viewing Manchuria and Mongolia as important strategic directions for the nation and seeking to establish a monopoly over the region. During the 1920s, Japan's policies in this regard underwent significant fluctuations. Initially, the Hiranuma Diplomacy shifted away from the military coercion and interference in China's internal affairs during World War I, proposing the so-called “non-interference in China's internal affairs” and “coordination among great powers” as diplomatic principles. However, after the formation of the Tanaka Cabinet, Japan abandoned this “non-interference policy” and adopted an aggressive policy toward China [13]. Nevertheless, its core objective remained the occupation of Manchuria and Mongolia to strengthen its presence in Northeast Asia.

In Northeast Asia, Japan and the Soviet Union were the two major powers with decisive strength, and thus jointly dominated the regional landscape in the 1920s, dividing up the region's resources and interests. As stated in Article 2 of the Treaty between Japan and the Soviet Union on the Basic Rules Governing Relations between the Two Countries, signed on January 20, 1925: The Union of Soviet Socialist Republics agrees that the Treaty of Portsmouth of September 5, 1905, shall remain in effect," and agreed to review, amend, or abolish other treaties from the pre-revolutionary Russian period [14]. However, since neither side possessed the capability to completely defeat the other, the two nations maintained a balance of power in Northeast Asia, resulting in a relatively stable situation during that period.

4.2.2. The relative constraints of international treaties and systems

In the context of power balance, as in the Vienna System, international treaties and the international system formed by them constitute an important component of it. Within the framework of modern international law, international treaties and the international system generally exert a certain degree of constraint on relevant states. In the 1920s, the Washington System and the Nine-Power Treaty, along with a series of resolutions related to China, were closely connected to China, or Northeast Asia. Among these, the Nine-Power Treaty, officially titled the Treaty of the Nine Powers Concerning the Principles and Policies to Be Applied to Chinese Affairs, was the most important document adopted at the Washington Conference regarding China. The Nine-Power Treaty stipulated: (1) Respect for China's sovereignty, independence, and territorial and administrative integrity; (2) Providing China with full and unimpeded opportunities to develop and maintain a strong and stable government; (3) Making every effort to protect the principle of equal business and industrial opportunities for all countries within China; (4) Not to take advantage of China's current situation to seek special or preferential rights that would diminish the rights of friendly nations, nor to encourage actions harmful to the security of friendly nations. Additionally, the treaty prohibits countries from privately concluding treaties that infringe upon China's interests; reaffirms the principles of open doors and equal opportunities in commerce; prohibits the division of spheres of influence within China's territory; ensures fair use of China's railways; and respects China's right to neutrality [15]. From this, it is clear that the treaty does not tolerate or accept any form of exclusive control over China.

The Nine-Power Treaty essentially embodied the spirit of US policy toward China and dealt a blow to Japan's attempts to dominate China. The framework it established was known as the Washington System, which maintained stability in the Pacific and Far East for nearly a decade [16]. This also helped maintain relative stability in Northeast Asia during the 1920s. Although the binding power of treaties and systems is not strong, far inferior to the constraints imposed by the power balance formed by national strength, within the framework of international law, the boundaries and rules established by international treaties and systems are often recognized and adhered to by signatory nations within a certain timeframe, thereby exerting a certain degree of constraint. This played a significant role in maintaining the stable situation of the period.

4.3. Other special power balance factors

4.3.1. The growth of local power in Northeast China and its foreign policy

In the 1920s, the military power of the Fengtian clique, a local faction in Northeast China, grew significantly. After Shikai Yuan's death in 1916, the Beiyang warlords split into three major factions. Zuolin Zhang, who held the positions of military governor and provincial governor of Fengtian, wielded considerable military power and established his own faction. The Fengtian warlords relied on Japanese imperialism as their backing and by 1919 had completely controlled the three northeastern provinces. During the Zhili-Anhui War in 1920, Zuolin Zhang allied with the Zhili warlords to overthrow the Qirui Duan government and was appointed Inspector-General of the Three Northeastern Provinces. In 1922, the Fengtian faction was defeated in the First Zhili-Fengtian War, and Zuolin Zhang retreated beyond the Great Wall. In 1924, he defeated the Zhili faction in the Second Zhili-Fengtian War and, together with Yuxiang Feng, took control of the Beijing government. Thereafter, the Fengtian warlords' power gradually expanded, their influence grew, and they commanded hundreds of thousands of troops, extending their influence to Shanghai, Jiangsu, and other regions, and in 1926, they took control of the Beijing government. Even after the Huanggutun Incident, when Xueliang Zhang took over affairs in Northeast China and the region changed its allegiance, the military strength of Northeast China remained the second strongest in the country, surpassed only by Chiang Kai-shek's Central Army. Their formidable strength enabled the Fengtian warlords to resist the impact of Japan and Russia to a certain extent and stabilize the situation in Northeast China.

As a local power, Zuolin Zhang and his son Xueliang Zhang also sought to maintain a balanced foreign policy, avoiding excessive reliance on any one side. Initially, Zuolin Zhang maintained close ties with Japan. With Japan's support and assistance, he was able to fully control the three northeastern provinces and establish himself as the “King of Manchuria,” which also aligned with Japan's strategic objectives at the time. However, once Zuolin Zhang's power had grown significantly, he no longer blindly followed Japan's lead and adopted a more assertive stance toward Japan compared to earlier periods. At the same time, Zuolin Zhang actively developed relations with the Soviet Union. In the same year that the Sino-Soviet Agreement was signed, he signed the Fengtian-Soviet Agreement with the Soviet government as a supplement to the Interim Agreement on the Administration of the China-Eastern Railway, allowing the Northeast region to negotiate with the Soviet Union on matters related to the China-Eastern Railway. Although this later led to disputes and even war, it remains a classic example of the Northeast region's efforts to develop relations with the Soviet Union. After Xueliang Zhang took over, he further strengthened ties with the central government, fully embodying the principle of balance. Under this “balancing act”-style foreign policy, the Northeast region maintained appropriate relations with Japan, the Soviet Union, and the Chinese government, carefully preserving peace and stability in the Northeast during the 1920s.

Although the local powers in Northeast China were relatively strong and had some connection with the theory of power balance, their strength was not sufficient to rival that of Japan and the Soviet Union, nor could they form a balance of power with them. This was inconsistent with traditional power balance theory. Therefore, in this paper, we treat them as a special factor in China and analyze their growth in strength and foreign policy to further examine the domestic factors contributing to the relative stability of Northeast Asia in the 1920s from a local perspective.

4.3.2. The policies and interventions of western powers outside the region

Traditional power balance theory primarily defined the relationships and patterns among countries within a region and did not address countries outside the region. Unlike traditional theory, due to the complexity of the situation in modern China, China at that time faced intervention from Western powers and other countries outside the region and lacked independence and autonomy. Therefore, examining the policies and interventions of Western powers outside the region is crucial to studying the patterns in Northeast Asia in the 1920s. Interestingly, during this period, Western powers in Europe and America also implemented an evolving power balance policy in Northeast Asia.

After World War I, three trends emerged in the development of China, Japan, and Russia: China, despite its weak strength, became more awakened; Japan gained enormous benefits and greatly increased its strength; and Russia was severely damaged by World War I, civil war, and intervention by the great powers, gradually distancing itself from the Western world. The previous power balance in Northeast Asia no longer existed. The shifting balance of power among the three nations prompted the Western powers, led by Britain and the United States, to adjust their policies toward the East Asian balance of power. As Balaklav put it: “Especially after the Russian Revolution of 1917, Japan was more likely to establish its own advantage. Just as in Europe, the war had a revolutionary impact on the power dynamics in the Far East. By 1918, even before the European war had ended, Wilson was already preparing to challenge Japan's expansion” [17].

In order to establish a power balance in Northeast Asia, Britain ultimately abandoned its original alliance with Japan. Together with the United States and France, Britain forced Japan to accept restrictions on its naval power at the Washington Conference and demanded that Japan relinquish its illegal occupation of territory and privileges in Shandong, China. From the perspective of power balance, the Washington System served as a counterweight to Japan to a certain extent before China and the Soviet Union were able to fully establish a power balance against Japan [18]. From the results, it is evident that the European and American powers' strategy of containing Japan through a power balance had a certain effect. In the 1920s, despite the three military interventions in Shandong during the Tanaka Cabinet, the overall situation in Northeast Asia and the relations among China, Japan, and the Soviet Union remained relatively calm, which played a significant role in maintaining the relative stability of the region.

5. Conclusion

In the 1920s, the situation in Northeast Asia was relatively stable due to a variety of factors. The formation and evolution of this situation involved complex geopolitical games and international relations, which had a profound impact on the regional and global situation.

The relatively stable situation in Northeast Asia during the 1920s was shaped by a combination of factors. The principle of power balance played a significant role: major regional powers such as Japan and the Soviet Union (USSR), leveraging their strong national strength, dominated Northeast Asia while also mutually restraining one another, thereby maintaining relative stability in the region during the 1920s; The Nine-Power Treaty and the Washington System it established, as international law, imposed relative restrictions on major powers in the region, particularly Japan, thereby constraining their behavior to some extent and maintaining the relatively stable situation. Additionally, beyond traditional power balance theory, due to China's unique circumstances during the modern era, there were other special power balance factors at play: First, the growing strength of local forces in Northeast China, represented by the Fengtian warlords, and their balanced foreign policy, maintained stable relations with all parties, preserving relative peace in the Northeast during the 1920s; Western powers from outside the region, represented by Britain, France, and the United States, implemented a promptly adjusted balance of power policy in Northeast Asia, intervening in the region's international situation. After World War I, they contained Japan's expansionist ambitions, maintaining stability in Northeast Asia. Therefore, the relatively stable situation in Northeast Asia during the 1920s was complex, influenced by multiple factors, with the power balance playing a pivotal role.

However, this relatively stable situation was clearly fragile and limited, being the product of a compromise between the interests of the great powers, and concealing deep contradictions and conflicts. Militarist forces within Japan continued to expand, dissatisfied with the existing system and seeking to break free from its constraints; the Soviet Union's strategic layout in Northeast Asia was also affected by changes in the international situation; and China, weakened by its declining national strength, found itself in a passive position, with its sovereignty and interests continuing to be infringed upon. With the changing international political and economic landscape, by the late 1920s, factors such as the impact of the Great Depression and the full-scale rise of Japanese militarism completely shattered the status quo in Northeast Asia. The relatively stable situation rapidly collapsed, giving way to Japan's full-scale invasion of China and the outbreak of World War II in the Far East.

Overall, the relative stability in Northeast Asia in the 1920s was the result of multiple factors, providing an important historical case study for research on power balance, interest competition, and regional security in international relations. Its formation, development, and collapse suggest that true regional stability cannot rely on fragile equilibrium and compromises between great powers. Only international relations based on fairness, equality, and mutual benefit, coupled with the continuous enhancement of national strength, can achieve lasting peace and stability.