Prior to Hitler declar­ing war on Poland, start­ing World War II's European the­ater, Japan was embroiled in its own con­flicts. Offi­cially, the Second Sino-Japanese War caused Japan to focus much of its resources on the Chinese front. Unof­fi­cially, there were two other fronts which pre­oc­cu­pied Japanese focus at the same time: the home front and the Soviet front. Due to ide­o­log­i­cal dif­fer­ences in their mil­i­tary, the country could not focus 100% of its eco­nomic and mil­i­tary on any front without com­plaints from other fac­tions. By fail­ing to ade­quately address the Soviet front for much of the Second Sino-Japanese War, the USSR not only posed as an active border threat to Man­chu­kuo, but also sent mil­i­tary sup­plies to China. Thus, the Japanese found themselves in an unof­fi­cial war on three fronts, drain­ing their mil­i­tary poten­tial and capa­city prior to the German inva­sion of Poland. Their aggres­sion against South­east Asia and the United States in order to gain resources to con­tinue their war machine was caused by Japan's inabil­ity to solve all three prob­lems of fac­tion­al­ism, China, and the Soviet Union until it was too late.

Before delv­ing into the com­plex retelling of Japan's fac­tion­al­ism in the 1930s, it is neces­sary to point out the his­to­ri­o­graph­i­cal com­plex­ity regard­ing the sub­ject. Crowley's "Japanese Army Fac­tion­al­ism in the 1930s" pro­vides an excel­lent sum­mary of the his­to­ri­o­graph­i­cal issues in the begin­ning of the article. Crowley noted that Japanese his­to­ri­ans rarely reveal the exact source of their infor­ma­tion, making judging sec­ondary sources dif­ficult. Much of the infor­ma­tion on Japan's war fac­tions came from the Tokyo Inter­na­tional Mil­i­tary Tri­bunal after the end of World War II. The pri­mary aim of the tri­bunal was to prove that mil­i­tary cliques were res­pon­si­ble for Japanese mil­i­tary aggres­sion prior to World War II. It was not based on pri­mary sources in the 1930s, but mostly on volun­tary tes­ti­mony from Gen­eral Tanaka Ryukichi. Other major sources of infor­ma­tion col­lected in the inves­ti­ga­tion included Muranaka Koji and Isobe Tokuichi's Views on the House­clean­ing of the Army, Iwabuchi Tatsuo's "A Geneal­ogy of Mil­i­tary Cliques," and Majima Ken's Secret His­tory of the Feuds between the Mil­i­tary Cliques. Accord­ing to Crowley, the oral tes­ti­mony was extracted for the spe­cif­ic purpose of pros­e­cut­ing Japanese leaders, and most of the other doc­u­ments showed bias. Each doc­u­ment also revealed the depth of Japan's fac­tional prob­lems in the back­ground of its rise in the 1930s.

General Tanaka Ryukichi recalled the infighting in the Japanese Imperial Army between two factions: the Toseiha (Control Group), and the Kodoha (Imperial Way Faction). The Control Group favored Nazi Germany's governance, while the Imperial Way Faction believed in the religious legitimacy of the Emperor as the head of Japan. The Control Group contained the likes of Generals Tetsuzan Nagata and Hideki Tojo. Meanwhile, the Imperial Way Faction was led by Generals Sadao Araki and Jinzaburo Masaki. When Japan favored the Control Group's ideas in 1934-35, this lead to vital younger members of Imperial Way Faction to rebel on February 26th, 1936. When their rebellion was crushed, the older members of the faction resigned in disgrace. Tanaka further claimed that most of the assassinations and intrigue which plagued Japan's army in the 1930s was due to the two factions' rivalry.

In contrast, Koji and Tokuichi's pamphlet indicated that there were four factions in the military, rather than two. Their publication was a polemic against people who were against Generals Araki and Masaki. Yet, Koji and Tokuichi did not explicitly refer to a "Kodoha" faction. Instead, they labelled four cliques in the military: the Arakiha (Araki's Group), the Seigunha (Purification Group), the Control Group, and the Seinen Shoko (young officers). The Purification Group was for the removal of all cliques in the army, while the young officers ended up being the rebellious members in the attempted February 26th coup.

Further complicating the military faction situation were Iwabuchi and Majima's accounts. They also created documents discussing four factions in the military. Iwabuchi, however, discounted factions solely supporting Araki or Masaki, but concurred on the existence of the Purification Group and a Control Group. Iwabuchi detailed two attempted coups in 1931, in which the Cherry Society attempted a coup d'etat to transfer power from the emperor to the military. Majima's account was based on a cumulative 17-hour conversation with General Masaki, and concluded that there were four factions: The Purification Group, the Imperial Way Faction, the Control Group, and the Kokutai Genriha (National Principles Group). The National Principles Group were intense believers of the Emperor's religious legitimacy, who were identified by Crowley as the perpetrators of multiple assassinations and the attempted 1936 coup.

Regardless of the historical accuracy of these factions, it is evident that Japan was plagued by factional infighting in the early-to-mid 1930s. These effects were not only felt within Japan's internal power structure, but affected foreign policy as well. A prime example occurred in that decade, as their armed forces were split in support of two ideological "defensive" strategies: the Hokushin-ron (Northern Expansion Doctrine) and the Nanshin-ron (Southern Expansion Doctrine).

Most of the army were advocates of the Northward Expansion Doctrine, though factions differed on which land to prioritize first. The end goal of this doctrine was to take Manchuria and Siberia in order to curtail Soviet threats. Japan also had high hopes regarding the natural resource potential of both territories, providing abundant raw materials for both Japan's economic and military benefit. According to Richard Samuels, the Imperial Way Faction sought a preemptive strike against the Soviet Union. In contrast, the Control Faction favored a cautious defensive expansionist approach prioritizing China instead of focusing on the USSR. Following the 1936 failed coup by younger members of the Imperial Way Faction, the Control Faction seized much control and guided army strategy. That is one of the primary reasons why Japan ended up waging war on China soon after, rather than the Soviet Union.

Meanwhile, most of the navy supported the Southward Expansion Doctrine, which prioritized Southeast Asia, the Dutch Indies, and the Phillipines. Those areas contained oil, which was vital as continued Japanese aggression could limit oil being imported from other countries. After all, Japanese naval ships required oil to run their operations. This strategy became more popular in the late 1930s, as the navy compromised with the army to support its land-based initiatives in exchange for a drastic increase in the naval budget. Aggressive action against French Indochina, the Dutch East Indies, and the United States were conducted based on the Southward Expansion Doctrine.

Combined with the divided nature of Japanese military politics, this led military leaders and groups to make aggressive foreign policy decisions without prior approval of the government. For instance, during the Second Sino-Japanese War, the Imperial Navy autonomously seized a number of Chinese islands for strategic reasons. In terms of the army, one of the more famous instances was the Kwantung Army's seizure of Manchuria in 1931.

The Kwantung Army, initially formed to protect Japanese interests on the Liaodong Peninsula, was influenced by radical thinkers such as Ikki Kita. Though Kita was executed following the 1936 attempted coup, this made him a nationalistic martyr. Kita, in his "An Outline Plan for the Reorganization of Japan" argued for massive internal reorganization, as well as an aggressive expansionist strategy to prevent Japanese overpopulation and liberation of Asian peoples under Western Imperial nations. Kita argued first for a suspension of the Japanese Constitution for three years, the dissolving of the two legislative houses, and the implementation of martial law. This would clear the way for the Japanese military to achieve its strategic needs. The emperor would still exist, but would have a fifty-person advisory council assisting him in executing Japan's goals. Kita encouraged expansion into eastern Siberia and Australia. He justified military aggression against other powers as a war of liberation against Western Imperialism, which included wars to liberate Manchuria from both ideological and literal occupiers. Members of the Kwantung Army used this as sufficient justification for expansionist aggression in Manchuria.

This unilateral conquest of Manchuria was primarily done to ease economic troubles in Japan, as well as executing the first step in the Northern Expansion Doctrine. Manchuria contained thousands of miles of railways owned by China, the Soviet Union, and Japan. The territory held a vast abundance of mineral and agricultural resources. Major E.W. Polson Newman argued that not only was Manchuria vital to Japanese industry, it also provided a bulwark against foreign threats. That was why even before its seizure, Japan placed 15,000 troops there to guard its railways. On September 18th, 1931, key figures in the Kwantung Army, including Colonel Itagaki Seishiro, Lieutenant Colonel Ishihara Kanji, Colonel Doihara Kenji, and Major Tanaka Takayoshi, purposefully detonated dynamite near a Japanese railway in Manchuria. Even though the dynamite failed to destroy the track, the Imperial Japanese Army, unaware of the Kwantung plot, blamed Chinese dissidents for the act. Within the next six months, Japan invaded and seized Manchuria. Manchukuo, thus, was made into a puppet state. Once Japan discovered the detonation was caused by the Kwantung Army, members of the government attempted to punish them, yet this discipline was not performed, and the Kwantung Army's actions eventually received endorsement and praise from much of the Japanese government. Chung-in Moon and Seung-Won Suh noted that endorsing such insubordination created a "system of irresponsibility" in Japan.

Another consequence of Japan's divided foreign policy was their inability to peacefully solve the Soviet threat following the establishment of Manchukuo. Even though the Soviet Union owned railways in Manchuria and had large amounts of troops stationed in their border with China, they held a "non-intervention policy" toward Japanese aggression. The USSR even formally acknowledged Manchukuo's creation, and conducted trade negotiations regarding the Chinese portion of the railway. Sha Qingqing argued that the lack of Soviet intelligence on northeastern China played a contributing role. They did not know of the Kwantung Army's plot or intentions to seize all of northeastern China. The USSR also overestimated Japan's strength prior to the Manchurian invasion. One of Stalin's main objectives was national security. If he believed that taking advantage of conflicts between two neighboring powers would increase Soviet national security, Stalin would initiate policies to ensure the USSR's security. He also feared that the Japanese aggression preluded a concerted assault from the Western powers on the USSR. This is why he even offered a Soviet-Japanese non-aggression pact in late 1931. Had Japan accepted it, then the USSR probably would not have aided China in the Second Sino-Japanese War.

Yet, Imperial Japan chose not to peacefully solve the Soviet problem. If Japanese military policy adopted the Control Faction's strategy, the Japanese could have solely focused on China as a military goal. The Second Sino-Japanese War could have been very different if Japan focused all its resources on China, while keeping a non-aggression pact with the Soviet Union. Instead, because members of the Imperial Way Faction still held influence, Siberia was still seen as a priority military goal for Japan. After Manchukuo was established, Japan reinforced the puppet state with 100,000 soldiers and conducted intelligence operations on the Soviet Union for a presumable future invasion.

This ignited Stalin's suspicions on the potential Japanese threat to his borders. Through intercepted dispatches, he became aware of Japanese aggressive intent to the Soviet Union. It appeared that the Manchurian takeover was the first step of a future invasion of the USSR. Molotov addressed this potential threat in late December of 1931. This affected Soviet foreign policy, and caused Stalin, in 1932, to sign treaties with Poland and other Baltic nations to shore up his western front. Japan still had chances to peacefully resolve the Soviet problem, as Stalin was still open to a non-aggressive pact with Japan even in 1933. Even though the Japanese central government did not, under any circumstance, desire war with the Soviet Union, the Kwantung Army remained hostile to Russia. Therefore, the Japanese continued to conduct clandestine operations against their northern neighbor. Hiroaki Kuromiya and Georges Mamoulia detailed multiple intercepted communications between Japanese intelligence and minority groups in the USSR. Japan even aimed for a grand Muslim alliance throughout Soviet territory to rebel against Stalin. If not for a strong counter-intelligence system, the Soviet Union may well have undergone a civil war caused by Japan's espionage efforts. Thus, when Trotskyiest and Zinoviniest forces tried to assassinate Soviet leaders, Stalin knew that Japan played a part in encouraging their efforts. In combination with Japan signing the Anti-Comintern treaty with Germany, this further increased suspicion that Japan and Germany were going to attack the USSR together.

Thus, it is not surprising that the Soviet Union aided China for much of the Second Sino-Japanese War. The USSR and China did not always have a rosy relationship. In the 1920s, the Soviet Union formed a Comintern with Chinese Communist Party (CCP), supporting their attempted takeover of the Chinese government. This attempt failed due to Nationalist leader, Jiang Jieshi, successfully purging thousands of Communists in the late 1920s. Soviet support of China was certainly not based on ideology, nor was it based on economic reasons, as the Soviet Union sold the Eastern Chinese Railway to Manchukuo without Chinese approval. The USSR further angered Jiang Jieshi by creating the Mongolian People's Republic, bringing Soviet troops into Mongolia to promote that country without Chinese approval. It was solely due to their mutual suspicions and hostility towards Japan that the USSR aided China.

From a military perspective, Jiang Jieshi had relatively little choice in obtaining Soviet help. In the beginning of the Sino-Japanese War in 1937, Japan's firepower outnumbered China's by four-to-five times. The main numerical disparity lay in their respective aerial capacities and armored cavalry: Japanese planes outnumbered Chinese planes by thirteen times; Japanese tanks outnumbered Chinese tanks by 36 times. At the same time, China faced an ideological civil war between the Nationalists and the CCP. Jiang could not request aid from the United States, because most Americans did not care about Japanese aggression against the Chinese in 1937. Claire Lee Chennault, a retired American aviator helping the Chinese air force at the time, argued that America was not enforcing its "Open Door Policy." Continuance in supplying Japan with oil was proof that the U.S would not aid China at the beginning of the Second Sino-Japanese War. With no hope from America, Jiang signed a non-aggression pact with Stalin on August 21st, 1937. The Soviet Union began supplying weapons to China in October 1937, and finalized two loans of $50 million and $150 million within the next two years. From 1937 to 1939, China received 985 airplanes, 82 tanks, 1,300 cannons, and more than 14,000 machine guns. These weapons alone greatly aided China in their fight against Japan.

Not only did the Soviet Union supply China with weapons, they also unofficially provided human support as well. The USSR agreed to send military advisors, specialists, and volunteer pilots. By 1939, there were 3,665 Soviet military specialists fighting against the Japanese on China's side. A prime example of their effect on Chinese defense was through the air force. Japan battered China's already weak air force in the beginning stages of the Second Sino-Japanese War. This meant that their bombers could wreak havoc on Chinese supply lines and cities. When the volunteer Soviet pilots arrived, even in unfamiliar territory, they reinforced China's air defense. In one instance, F. P. Polynin and his pilots launched a bombing raid against a Japanese aerodrome in Taiwan. Through deception, they successfully dropped 280 bombs which hit the assigned targets. According to Yu V. Chudodeev, more than 200 volunteer pilots were killed in the Second Sino-Japanese War.

With aid from the Soviet Union, Japan incurred a large amount of casualties and costs in their war against China. China scored a large defeat against Japan at the Battle of Taierzhuang in 1938, resulting in a large morale boost for the Chinese forces as well as the shattering of Japanese military invincibility. This battle delayed the Japanese advance into the Chinese mainland for months. Even the successful capture of Wuhan was costly for the Japanese. While China lost a million soldiers, Japan lost hundreds of thousands of troops, as well as hundreds of airplanes. Stephen MacKinnon noted that China's defense of Wuhan though unsuccessful garnered significant international press. Newspapers such as the New Republic portrayed the defense of Wuhan as a defense of Republicanism against Fascism. Poets and writers visited China just to write publications on China's heroic defense. With the world focused on the Second Sino-Japanese War, Japan realized that a successful Chinese campaign required greater costs than they had realized. MacKinnon argued that these mounting casualties and costs led Japan to once again focus their attention on their Soviet neighbors.

Due to both Soviet interference in the Second Sino-Japanese War and their establishment of the Mongolian People's Republic, Japan and the Soviet Union unofficially fought each other during the Battle of Khalkin Go in 1939. Mongolia was always key as a potential buffer to the Soviet Union. The Kwantung Army constructed watch posts and sent in spies in order to win the Mongols from the Soviets. Japan demanded the creation of representative offices in Outer Mongolia, but the Mongolian government resisted. Seeing that the Soviet Union was supporting Mongolia, Japan sought to achieve two objectives at once: to seize Mongolia and to deter the Soviet Union from supporting China. This culminated in the Battle of Khalkin Go, leading to a turning point in Japanese war strategy.

Khalkin Go contained four stages: the gathering of Japanese forces in April and May, the victories by this offensive from late May to July, the successful counterattack by Mongolian-Soviet forces and a hiatus to gather reinforcements, and finally the "almost total" annihilation of the Japanese-Manchukuo army. In April and May, Japan openly amassed 3,000 soldiers on the Manchukuo-Mongolian border. Clashes between Japanese and Mongolian forces occurred sporadically in those two months. When a Soviet platoon attempted to reconnoiter the situation on May 22nd , they were attacked and repelled by Japanese cavalry. With Japanese forces ready, the second stage of the conflict occurred when they began trying to encircle and destroy the Soviet and Mongol forces in eastern Mongolia. The Soviet-Mongol army fell back, and stopped the offensive with their artillery. This caused a hiatus in fighting, leading to the third phase when both Japanese and Soviet-Mongol reinforcements arrived in June and July. Japan now had 20,000 infantry, 4700 cavalry, 130 tanks, and 225 planes. In comparison, the Soviet-Mongol army 12,500 units, some number of anti-tank guns, and 500 armored vehicles. Under the command of General Georgy Zhukov, the Soviet-Mongol forces utilized their armored superiority, successfully flanking and repelling the Japanese advance. Zhukov was sent directly by Stalin in order to take command of the situation. He adapted a plan to encircle and eliminate the Japanese. At this time, Japan decided to place 100,000 troops to continue their Mongolian offensive, but the Soviet-Mongol forces launched their own offensive, almost shattering the Japanese forces. At the end of the battle, Japan lost 52,000-55,000 men. With the failure of Japan's initiative against the Soviet Union, the Japanese was forced to reevaluate their entire expansion strategy.

With rising costs from the Second Sino-Japanese War, along with the failure to take Mongolia and contest the Soviet Union, the navy asserted its influence on Japanese strategy. Japan's military adopted the Southern Expansionist Doctrine in order to gain valuable raw materials and oil to continue their military campaigns. Once they took French Indochina at the beginning of World War II, this was seen as an unwarranted aggression by the United States. As a consequence, America embargoed Japan, leaving Japan little choice but to plan an attack on the United States.