In 1917 China declared war on Germany in the hope of recovering its lost province, then under Japanese control. But in 1918 the Beijing government signed a secret deal with Japan accepting the latter's claim to Shandong. When the Paris peace conference of 1919 confirmed the Japanese claim to Shandong and Beijing's sellout became public, internal reaction was shattering. On May 4, 1919, there were massive student demonstrations against the Beijing government and Japan. The political fervor, student activism, and iconoclastic and reformist intellectual currents set in motion by the patriotic student protest developed into a national awakening known as the May Fourth Movement (). The intellectual milieu in which the May Fourth Movement developed was known as the New Culture Movement and occupied the period from 1917 to 1923. The student demonstrations of May 4, 1919 were the high point of the New Culture Movement, and the terms are often used synonymously. Students returned from abroad advocating social and political theories ranging from complete Westernization of China to the socialism that one day would be adopted by China's communist rulers.

Opposing the Warlords

The May Fourth Movement helped to rekindle the then-fading cause of republican revolution. In 1917 Sun Yat-sen had become commander-in-chief of a rival military government in Guangzhou () in collaboration with southern warlords. In October 1919 Sun reestablished the Guomindang to counter the government in Beijing. The latter, under a succession of warlords, still maintained its facade of legitimacy and its relations with the West. By 1921 Sun had become president of the southern government. He spent his remaining years trying to consolidate his regime and achieve unity with the north. His efforts to obtain aid from the Western democracies were ignored, however, and in 1921 he turned to the Soviet Union, which had recently achieved its own revolution. The Soviets sought to befriend the Chinese revolutionists by offering scathing attacks on "Western imperialism." But for political expediency, the Soviet leadership initiated a dual policy of support for both Sun and the newly established Chinese Communist Party ( CCP). The Soviets hoped for consolidation but were prepared for either side to emerge victorious. In this way the struggle for power in China began between the Nationalists and the Communists. In 1922 the Guomindang-warlord alliance in Guangzhou was ruptured, and Sun fled to Shanghai (). By then Sun saw the need to seek Soviet support for his cause. In 1923 a joint statement by Sun and a Soviet representative in Shanghai pledged Soviet assistance for China's national unification. Soviet advisers--the most prominent of whom was an agent of the Comintern, Mikhail Borodin--began to arrive in China in 1923 to aid in the reorganization and consolidation of the Guomindang along the lines of the Communist Party of the Soviet Union. The CCP was under Comintern instructions to cooperate with the Guomindang, and its members were encouraged to join while maintaining their party identities. The CCP was still small at the time, having a membership of 300 in 1922 and only 1,500 by 1925. The Guomindang in 1922 already had 150,000 members. Soviet advisers also helped the Nationalists set up a political institute to train propagandists in mass mobilization techniques and in 1923 sent Chiang Kai-shek ( Jiang Jieshi in pinyin), one of Sun's lieutenants from Tongmeng Hui days, for several months' military and political study in Moscow. After Chiang's return in late 1923, he participated in the establishment of the Whampoa ( Huangpu in pinyin) Military Academy outside Guangzhou, which was the seat of government under the Guomindang-CCP alliance. In 1924 Chiang became head of the academy and began the rise to prominence that would make him Sun's successor as head of the Guomindang and the unifier of all China under the right-wing nationalist government.

Sun Yat-sen died of cancer in Beijing in March 1925, but the Nationalist movement he had helped to initiate was gaining momentum. During the summer of 1925, Chiang, as commander-in-chief of the National Revolutionary Army, set out on the long-delayed Northern Expedition against the northern warlords. Within nine months, half of China had been conquered. By 1926, however, the Guomindang had divided into left- and right-wing factions, and the Communist bloc within it was also growing. In March 1926, after thwarting a kidnapping attempt against him, Chiang abruptly dismissed his Soviet advisers, imposed restrictions on CCP members' participation in the top leadership, and emerged as the preeminent Guomindang leader. The Soviet Union, still hoping to prevent a split between Chiang and the CCP, ordered Communist underground activities to facilitate the Northern Expedition, which was finally launched by Chiang from Guangzhou in July 1926.

In early 1927 the Guomindang-CCP rivalry led to a split in the revolutionary ranks. The CCP and the left wing of the Guomindang had decided to move the seat of the Nationalist government from Guangzhou to Wuhan. But Chiang, whose Northern Expedition was proving successful, set his forces to destroying the Shanghai CCP apparatus and established an anti-Communist government at Nanjing in April 1927. There now were three capitals in China: the internationally recognized warlord regime in Beijing; the Communist and left-wing Guomindang regime at Wuhan (); and the right-wing civilian-military regime at Nanjing, which would remain the Nationalist capital for the next decade.

The Comintern cause appeared bankrupt. A new policy was instituted calling on the CCP to foment armed insurrections in both urban and rural areas in preparation for an expected rising tide of revolution. Unsuccessful attempts were made by Communists to take cities such as Nanchang (), Changsh()), Shantou (), and Guangzhou, and an armed rural insurrection, known as the Autumn Harvest Uprising, was staged by peasants in Hunan Province. The insurrection was led by Mao Zedong ( 1893-1976), who would later become chairman of the CCP and head of state of the People's Republic of China. Mao was of peasant origins and was one of the founders of the CCP.

But in mid-1927 the CCP was at a low ebb. The Communists had been expelled from Wuhan by their left-wing Guomindang allies, who in turn were toppled by a military regime. By 1928 all of China was at least nominally under Chiang's control, and the Nanjing government received prompt international recognition as the sole legitimate government of China. The Nationalist government announced that in conformity with Sun Yat-sen's formula for the three stages of revolution--military unification, political tutelage, and constitutional democracy--China had reached the end of the first phase and would embark on the second, which would be under Guomindang direction.