The Warlord Era was a period in the history of the Republic of China when control of the country was divided among former military cliques of the Beiyang Army and other regional factions from 1916 to 1928. In historiography, the Warlord Era began in 1916 upon the death of Yuan Shikai, the de facto dictator of China after the Xinhai Revolution overthrew the Qing dynasty and established the Republic of China in 1912. Yuan's death created a power vacuum that spread across the Mainland China regions of Sichuan, Shanxi, Qinghai, Ningxia, Guangdong, Guangxi, Gansu, Yunnan and Xinjiang. The Nationalist Kuomintang government of Sun Yat-sen based in Guangzhou began to contest Yuan's Beiyang Government based in Beijing as the legitimate government of China. The Warlord Era was characterized by constant civil war between different factions, the largest of which was the Central Plains War which involved more than one million soldiers. The Warlord Era ended in 1928 when the Kuomintang under Chiang Kai-shek officially unified China through the Northern Expedition, marking the beginning of the Nanjing decade. Several of the warlords continued to maintain their influence through the 1930s and the 1940s, which was problematic for the Nationalist government during both the Second Sino-Japanese War and Chinese Civil War. Terminology During World War I the New Culture Movement leader Chen Duxiu introduced the term Junfa (軍閥), taken from the Japanese gunbatsu. It was not widely used until the 1920s, when it was taken up by left-wing groups to excoriate local militarists. Previously, these militarist leaders were known as a Tuchun (督軍), or provincial military governor, owing to the system Yuan Shikai introduced after his centralization of power. Origins The origins of the armies and leaders which dominated politics after 1912 lay in the military reforms of the late Qing dynasty. During the Taiping Rebellion (1850–1864), the Qing dynasty was forced to allow provincial governors to raise their own armies, the Yong Ying, to fight against the Taiping rebels; many of these provincial forces were not disbanded after the Taiping rebellion was over, like Li Hongzhang's Huai Army. Strong bonding, family ties and respectful treatment of troops were emphasized. The officers were never rotated, and the soldiers were handpicked by their commanders, and commanders by their generals, so personal bonds of loyalty formed between local officers and the troops, unlike Green Standard and Banner forces. These late Qing reforms did not establish