Following the collapse of the Qing dynasty and the 1911 Revolution, Sun Yat-sen assumed the presidency of the newly formed Republic of China (ROC), and was shortly thereafter succeeded by Yuan Shikai.^{[19][page needed]} Yuan failed in a short-lived attempt to declare himself emperor, and China fell into power struggle after his death in 1916.

The Kuomintang (KMT), led by Sun Yat-sen, created a new government in Guangzhou to rival the warlords who ruled over large swathes of China and prevented the formation of a solid central government.^[20] After Sun's efforts to obtain aid from Western countries were ignored, he turned to the Soviet Union. In 1923, Sun and Soviet representative Adolph Joffe in Shanghai pledged Soviet assistance to China's unification in the Sun–Joffe Manifesto, a declaration of cooperation among the Communist International (Comintern), KMT, and the Chinese Communist Party (CCP).^[21]

The CCP, which was initially a study group by Chinese intellectuals, was officially established in 1921 at the First National Congress in the French Concession in Shanghai, and the KMT jointly formed the First United Front, with the primary goal of defeating regional warlords, unifying China as well as sought to expel Western and Japanese imperialist powers who held control over Chinese ports and territories following the unequal treaties imposed after the Opium Wars, the First Sino-Japanese War and the Asian theater of World War I.^[20][21] Comintern agent Mikhail Borodin arrived in 1923 to aid in the reorganization and consolidation of both the Chinese Communist Party and the Kuomintang along the lines of the Communist Party of the Soviet Union.

In 1923, Sun sent Chiang Kai-shek, one of his lieutenants, for several months of military and political study in Moscow.^[22] Chiang then became the head of the Whampoa Military Academy that trained the next generation of military leaders. The Soviets provided the academy with teaching material, organization, and equipment, including munitions.^[22] They also provided education in many of the techniques for mass mobilization. With this aid, Sun raised a dedicated "army of the party", with which he hoped to defeat the warlords militarily. CCP members were also present in the academy, and many of them became instructors, including future communist premier Zhou Enlai, who was made a political instructor.^[23]

Communist members were allowed to join the KMT on an individual basis.^[21] The CCP itself was still small at the time, having a membership of 300 in 1922 and only 1,500 by 1925.^[24] As of 1923, the KMT had 50,000 members.^[24] However, after Sun died in 1925, the KMT split into left- and right-wing movements. Right-wing KMT members began to worry that the Soviets were trying to destroy the KMT from within using the CCP. In March 1926, Chiang Kai-shek, who had been made commander in chief of the KMT army, began the expulsion of communists from prominent positions, later known as the Canton Coup. The CCP then began movements in opposition of Chiang's leadership and the Northern Expedition, passing a resolution against it at a party meeting. Then, in March 1927, the KMT held its second party meeting where the Soviets helped pass resolutions against the Expedition and curbing Chiang's power. Soon, the KMT would be clearly divided.

In early 1927, the KMT–CCP rivalry led to a split in the revolutionary ranks. The CCP and the left wing of the KMT decided to move the seat of the KMT government from Guangzhou to Wuhan, where communist influence was strong.^[24] However, Chiang and Li Zongren, whose armies defeated the warlord Sun Chuanfang, moved eastward toward Jiangxi. The leftists rejected Chiang's demand to eliminate Communist influence within the KMT, and Chiang denounced them for betraying Sun Yat-sen's Three Principles of the People by taking orders from the Soviet Union. According to Mao Zedong, Chiang's tolerance of the CCP within the KMT camp decreased as his power increased.^[25]

On 7 April, Chiang and several other KMT leaders held a meeting, during which they proposed that Communist activities were socially and economically disruptive and had to be undone for the Nationalist revolution to proceed. On 12 April, many communists within the KMT were purged in Shanghai through hundreds of arrests and executions on the orders of General Bai Chongxi.^[20][26] The CCP referred to this as the 12 April Incident, known in the West as the Shanghai massacre, and the beginning of the White Terror.^[27] This incident widened the rift between Chiang and Wang Jingwei, the leader of the left wing faction of the KMT.

Under pressure from Chiang, the left wing of the KMT also began expelling CCP members from the Wuhan Government in July 1927, which in turn was toppled by Chiang Kai-shek. The KMT resumed its campaign against the warlords and captured Beijing in June 1928.^[28] Soon, most of eastern China was under the control of the Nanjing central government, which received prompt international recognition as the sole legitimate government of China. The KMT government announced, in conformity with Sun Yat-sen, the formula for the three stages of revolution: military unification, political tutelage, and constitutional democracy.^[29]

On 1 August 1927, the CCP launched an uprising in Nanchang against the Nationalist government in Wuhan in response to the Shanghai Massacre. This conflict led to the creation of the Chinese Red Army.^[30][31] On 4 August, the main forces of the Red Army left Nanchang and headed southwards for an assault on Guangdong. Nationalist forces quickly reoccupied Nanchang while the remaining members of the CCP in Nanchang went into hiding.^[30] A CCP meeting on 7 August confirmed the objective of the party was to seize political power by force, but the CCP was quickly suppressed the next day by the Nationalist government in Wuhan, led by Wang Jingwei. On 14 August, Chiang Kai-shek announced his temporary retirement, as the Wuhan faction and Nanjing faction of the Kuomintang were allied once again with common goal of suppressing the CCP after the earlier split. Wang Jingwei took the leadership of KMT after Chiang.^{[citation needed]}

Attempts were later made by the CCP to take the cities of Changsha, Shantou and Guangzhou. The Red Army, consisting of mutinous former National Revolutionary Army (NRA) soldiers as well as armed peasants, established control over several areas in southern China.^[31] KMT forces continued to attempt to suppress the rebellions.^[31] Then, in September, Wang Jingwei was forced out of Wuhan. September also saw an unsuccessful armed rural insurrection, known as the Autumn Harvest Uprising, led by Mao Zedong.^[32] Borodin then returned to the Soviet Union in October via Mongolia. In November, Chiang Kai-shek went to Shanghai and invited Wang to join him. On 11 December, the CCP started the Guangzhou Uprising, establishing a soviet there the next day, but lost the city by 13 December to a counter-attack under the orders of General Zhang Fakui. On 16 December, Wang Jingwei fled to France. There were now three capitals in China: the internationally recognized republic capital in Beijing, the CCP and left-wing faction of the KMT at Wuhan and the right-wing KMT regime at Nanjing, which would remain the KMT capital for the next decade.^[33][34] This marked the beginning of a ten-year armed struggle, known in mainland China as the "Ten-Year Civil War" (十年内战) which ended with the Xi'an Incident, when Chiang Kai-shek was forced to form the Second United Front against invading forces from the Empire of Japan.

In 1930, the Central Plains War broke out as an internal conflict of the KMT; launched by Feng Yuxiang, Yan Xishan, and Wang Jingwei. The attention was turned to root out remaining pockets of CCP activity in a series of five encirclement campaigns.^[35] The first and second campaigns failed, and the third was aborted due to the Mukden Incident. The fourth campaign (1932–1933) achieved some early successes, but Chiang's armies were badly mauled when they tried to penetrate into the heart of Mao's Soviet Chinese Republic. During these campaigns, KMT columns struck swiftly into CCP areas, but were easily engulfed by the vast countryside and were not able to consolidate their foothold. Finally, in late 1934, Chiang launched a fifth campaign that involved the systematic encirclement of the Jiangxi Soviet region with fortified blockhouses.^[36] The blockhouse strategy was devised and implemented in part by newly hired Nazi advisors.^[37] Unlike previous campaigns in which they penetrated deeply in a single strike, this time the KMT troops patiently built blockhouses, each separated by about eight kilometres (five miles), to surround the Communist areas and cut off their supplies and food sources.^[36]

In October 1934, the CCP took advantage of gaps in the ring of blockhouses (manned by the forces of a warlord ally of Chiang Kai-shek's, rather than regular KMT troops) and broke out of the encirclement. The warlord armies were reluctant to challenge Communist forces for fear of losing their own men and did not pursue the CCP with much fervor. In addition, the main KMT forces were preoccupied with annihilating Zhang Guotao's army, which was much larger than Mao's. The massive military retreat of Communist forces lasted a year and covered what Mao estimated as 12,500 km (25,000 Li; 7,800 mi); it became known as the Long March.^[38]

This military retreat was undertaken by the Chinese Communist Party, led by Mao Zedong, to evade the pursuit or attack of the Kuomintang army. It consisted of a series of marches, during which numerous Communist armies in the south escaped to the north and west. Over the course of the march from Jiangxi the First Front Army, led by an inexperienced military commission, was on the brink of annihilation by Chiang Kai-Shek's troops as their stronghold was in Jiangxi. The Communists, under the command of Mao Zedong and Zhou Enlai, "escaped in a circling retreat to the west and north, which reportedly traversed over 9,000 kilometres (5,600 mi) over 370 days." The route passed through some of the most difficult terrain of western China by traveling west, and then northwards towards Shaanxi.

In November 1935, shortly after settling in northern Shaanxi, Mao officially took over Zhou Enlai's leading position in the Red Army. Prior to this, Zhou had been the dominant military commander following the Zunyi Conference in January 1935. However, after Zhou contracted a severe case of amoebic dysentery in August 1935, Mao increasingly assumed the role of de facto military commander. Following a major reshuffling of official roles, Mao became the chairman of the Central Military Commission, with Zhou and Deng Xiaoping as vice-chairmen. This marked Mao's position as the preeminent leader of the CCP, with Zhou in second position to him.^{[citation needed]} The march ended when the CCP reached the interior of Shaanxi. Zhang Guotao's army (Red 4th Front Army), which took a different route through northwest China, was largely destroyed by the forces of Chiang Kai-shek and his Chinese Muslim allies, the Ma clique. Along the way, the Communist army confiscated property and weapons from local warlords and landlords, while recruiting peasants and the poor, solidifying its appeal to the masses. Of the 90,000–100,000 people who began the Long March from the Soviet Chinese Republic, only around 7,000–8,000 made it to Shaanxi.^[39] The remnants of Zhang's forces eventually joined Mao in Shaanxi, but with his army destroyed, Zhang, even as a founding member of the CCP, was never able to challenge Mao's authority. Essentially, the great retreat made Mao the undisputed leader of the Chinese Communist Party.

The Kuomintang used Khampa troops – who were former bandits – to battle the Communist Red Army as it advanced and to undermine local warlords who often refused to fight Communist forces to conserve their own strength. The KMT enlisted 300 "Khampa bandits" into its Consolatory Commission military in Sichuan, where they were part of the effort of the central government to penetrate and destabilize local Han warlords such as Liu Wenhui. The government was seeking to exert full control over frontier areas against the warlords. Liu had refused to battle the Communists in order to conserve his army. The Consolatory Commission forces were used to battle the Red Army, but they were defeated when their religious leader was captured by the Communists.^[40]

In 1931, the Empire of Japan invaded Manchuria. Although the Japanese expansionism in China posed a clear threat to both sides of the civil war, at first it did not lead to a cessation of hostilities.^[41] Rather, Chiang believed that "The Japanese are a disease of the skin. The Communists are a disease of the heart."^[42] He ordered his general in Manchuria not to resist the Japanese advance and instead focused on continuing the encirclement campaigns in the south.^[43] He called this policy "first internal pacification, then external resistance." (Chinese: 先安內，後攘外。)^[44][45] The CCP in turn reacted with disdain to Chiang's policy of nonresistance, viewing him as a pawn of the Japanese. They saw fighting the Nationalist government as an essential part of resistance to Japan and called for "Resisting Japan and Opposing Chiang".^[46][47] Nonetheless, prosecuting the civil war while also resisting Japan became increasingly impractical for the CCP in particular. Already by late 1932, Communist guerilla groups in Manchuria had begun to cooperate with Nationalist guerillas against the Japanese occupiers.^[48][49] The CCP also began to come under pressure from the Soviet Union to negotiate an end to the civil war. The USSR was concerned with events in Europe—especially Hitler's rise to power—and wanted Communist parties to form united fronts with moderates to resist fascist aggression. A united China was of particular importance to the USSR because it could be an important ally if Japan invaded the Russian Far East. This policy was formally adopted by the 7th World Congress of the Comintern in the summer of 1935.^[50]

The CCP delegation at the Congress, headed by Wang Ming, published the "August 1 Declaration" describing how a united front could be created in China. They recommended a government of national defense including all parties in China that wanted to resist Japanese imperialism.^[51][52][53] Importantly, because they still considered Chiang to be a "running dog" of the Japanese, they did not extend this offer to the Nationalist government.^[54] The CCP itself was in the middle of the Long March during the Comintern Congress and was cut off from radio communication with Moscow. Its leaders learned of the Congress's decisions in November 1935.^[53] The following month, they held a conference at Wayaobu to discuss the implications of this new Comintern policy. The Wayaobu Manifesto that they published was a significant retreat from the hardline positions they had held during the early civil war. It called for "the most broad national united front" to resist Japan, and announced that the CCP was willing to suspend class conflict in the interests of cross-class collaboration.^[55] However, they did not intend for the Chinese Red Army to surrender or submit to the Nationalists. On the contrary, their plan to resist the Japanese centered on expanding the Red Army to 1 million men and dramatically increasing the land area covered by the Chinese Soviet Republic.^[56]

In late 1935, relations between Nanjing and Tokyo took a sharp downturn as Japan stepped up its expansionist policies in northern China.^[57][58] Chiang Kai-shek feared that a full-scale invasion of China was imminent, and wanted to secure the material and diplomatic support of the Soviet Union.^[59] He also faced growing public pressure to actively resist Japan; on 9 December 1935, for example, a major anti-Japanese student protest broke out in Beiping.^[60][61][62] In January, Chiang Kai-shek sent his son Chiang Ching-Kuo to Moscow to negotiate a military mutual assistance treaty.^[63] However, as a precondition for a treaty, Chiang wanted the Soviet Union to order the CCP to submit to the Nationalist Government. The Soviet ambassador told Chiang that while the USSR hoped the CCP would agree to a unified command under the Nationalists, Chiang would have to negotiate directly with the CCP.^[64] This upset Chiang, who worried that if the USSR was unwilling to order the CCP to stop, they might be willing to support further revolutionary actions by the CCP if a ceasefire broke down. Progress halted, and after news leaked to the press that Chiang was contemplating a treaty with the USSR, he called off negotiations.^[65]

Meanwhile, the CCP opened up separate negotiations with the Nationalist forces besieging them in northwest China. They managed to sign secret ceasefire agreements with Zhang Xueliang, leader of the Northeastern Army, and Yang Hucheng, leader of the Northwestern Army.^[66] These generals were frustrated that Chiang was prioritizing civil war over resistance to Japan.^[67][68] Yan Xishan, another neighboring warlord, also signed a secret agreement with the Communists, although he was not as closely aligned with them as Zhang or Yang.^[69] The members of this northwestern alliance were united by their desire to resist Japan, but they differed over the details of how this could best be accomplished.^[66] The Communists supported a plan to use Soviet support to take over Shaanxi, Gansu, Ningxia, Qinghai, and Xinjiang and turn northwest China into a base under Zhang's command to resist Japan and oppose Chiang.^[70] Zhang, Yang, and Yan were still committed to convincing Chiang to lead the anti-Japanese resistance.^[66] As they continued to negotiate, they kept their alliance secret and even staged fake military battles to allay the suspicions of the Nanjing government.^[71][66]

Negotiations between Chiang and the CCP began in earnest in late 1936.^[72] Chiang continued to try to resolve the civil war militarily; he continued to consider a negotiated settlement with the CCP to be a last resort.^[73] He was encouraged by the results of the Ningxia campaign in mid-to-late October. In that campaign, the Second and Fourth Corps of the Red Army marched north to pick up supplies dropped in Mongolia by the Soviet Union, but found themselves trapped on the wrong side of the Yellow River.^[74] They were cut to pieces by the Hui cavalry allied with the Nationalists.^[75] Chiang began making preparations for a sixth encirclement campaign, and instructed Zhang and Yang to participate.^[76] In early November, Chen Lifu presented Pan Hannian with a set of extremely harsh conditions for a deal. The terms called for, among other things, reducing the Red Army to 3,000 men and sending all of its senior officers into exile.^[77][78] Pan balked, calling them "conditions for surrender".^[79] In late November, Chiang ordered the Northeastern Army and forces from the central Nationalist Army, Hu Zongnan's Right Route Army, to attack towards the Communist capital at Bao'an. At the resulting Battle of Shanchengbao, the Northeastern Army withheld most of its forces from the attack. This allowed the Red Army to ambush and nearly wipe out Hu's 78th regiment.^[80][81] This reversed the diplomatic situation: Chen Lifu moderated his conditions, but the CCP recalled Pan Hannian from Nanjing on December 10.^[82][83]

In late 1936, Zhang Xueliang decided that his repeated attempts to persuade Chiang to create a united front with the Communists were not going to be enough. To Zhang, Chiang appeared dead-set on continuing the civil war even as the threat of Japanese invasion loomed ever larger. Following Yang Hucheng's advice, he decided to resort to drastic measures.^[84][85] On 12 December 1936, the disgruntled Zhang and Yang conspired to kidnap Chiang and force him into a truce with the CCP. The incident became known as the Xi'an Incident.^[86] Both parties suspended fighting to form a Second United Front to focus their energies and fight the Japanese.^[86]