Between 1947 and September 22, 1949, Peng's forces occupied Gansu, Ningxia, and Qinghai. His forces repeatedly defeated but could not destroy the forces of Hu Zongnan and Ma Bufang, which retreated into Sichuan and were airlifted to Taiwan when the Kuomintang lost the Civil War in December 1949. In October Peng's forces, led directly by Wang Zhen, invaded Xinjiang. Most of Xinjiang's defenders surrendered peacefully and were incorporated as a new unit in Peng's army, but some ethnic guerrilla bands resisted Chinese control for several years. After the People's Republic of China was declared on October 1, 1949, Peng was appointed Chairman of the Northwest China Military and Administrative Commission and Commander-in-Chief and Political Commissar of Xinjiang, with Wang Zhen as his deputy. That appointment gave Peng responsibility over Shaanxi, Gansu, Ningxia, Qinghai, and Xinjiang, an area of over 5 million square kilometres (1.9 million square miles) but under 30 million people. Peng's forces continued their gradual occupation of Xinjiang, which they completed in September 1951.