The Republic of China (ROC) began on 1 January 1912 as a sovereign state in mainland China following the 1911 Revolution, which overthrew the Manchu-led Qing dynasty and ended China's imperial history. From 1927, the Kuomintang (KMT) reunified the country and ruled it as a one-party state with Nanjing as the national capital. In 1949, the KMT-led government was defeated in the Chinese Civil War and lost control of the mainland to the Chinese Communist Party (CCP). The CCP established the People's Republic of China (PRC) while the ROC was forced to retreat to Taiwan; the ROC retains control over the Taiwan Area, and its political status remains disputed. The ROC is recorded as a founding member of both the League of Nations and the United Nations, and previously held a permanent seat on the United Nations Security Council until 1971, when the PRC took China's seat in the United Nations General Assembly Resolution 2758. It was also a member of the Universal Postal Union and the International Olympic Committee. The ROC claimed 11.4 million km2 (4.4 million sq mi) of territory, and its population of 541 million in 1949 made it the most populous country in the world. The Republic of China was officially proclaimed on 1 January 1912 by revolutionaries under Sun Yat-sen, the ROC's founder and provisional president of the new republic, following the success of the 1911 Revolution. Puyi, the final Qing emperor, abdicated on 12 February 1912. Sun served briefly before handing the presidency to Yuan Shikai, the leader of the Beiyang Army. Yuan's Beiyang government quickly became authoritarian and exerted military power over the administration; in 1915, Yuan attempted to replace the Republic with his own imperial dynasty until popular unrest forced him to back down. When Yuan died in 1916, the country fragmented between local commanders of the Beiyang Army, beginning the Warlord Era defined by decentralized conflicts between rival cliques. At times, the most powerful of these cliques used their control of Beijing to assert claims to govern the entire Republic. Meanwhile, the KMT under Sun attempted multiple times to establish a rival national government in Guangzhou, eventually taking the city with the help of weapons, funding, and advisors from the Soviet Union under the condition that the KMT form the First United Front with the CCP. CCP members joined the KMT and the two parties cooperated to build a revolutionary base in Guangzhou, from which Sun planned to launch a campaign to reunify China. Sun's death in 1925 precipitated a power struggle that eventually resulted in the rise of General Chiang Kai-shek to KMT chairmanship. Chiang led the successful Northern Expedition from 1926 to 1928, benefitting from strategic alliances with warlords and the help of Soviet military advisors. By 1927, Chiang felt secure enough to end the alliance with the Soviets and purged the Communists from the KMT. In 1928, the last major warlord pledged allegiance to the KMT's Nationalist government in Nanjing. Chiang subsequently ruled the country as a one-party state (Dang Guo) under the KMT, receiving international recognition as the representative of China. While there was relative prosperity during the Nanjing decade (1927–1937), the ROC faced serious threats from within and without. After being severely weakened by the purge, the CCP gradually rebuilt its strength by organizing peasants in the countryside. In addition, warlords who resented Chiang's consolidation of power led several uprisings, most significantly the Central Plains War. In 1931, the Japanese invaded Manchuria, followed by a series of smaller encroachments and ultimately a full-scale invasion of China in 1937. World War II devastated China, leading to enormous loss of life and material destruction. War with Japan continued until their surrender in September 1945, after which Taiwan was placed under Chinese administration. Civil war then resumed, and the CCP's People's Liberation Army began to gain upper hand in 1948 over a larger and better-armed Republic of China Armed Forces due to better tactics and corruption within the ROC leadership. The CCP proclaimed the People's Republic of China in October 1949, though remnants of the ROC government would persist in mainland China until late 1951. Source: Wikipedia (en)