 Complete the following phrase:  During this time a series of wars took place in western China, including the Kumul Rebellion, the Sino-Tibetan War, and the Soviet Invasion of Xinjiang. Although the central government was nominally in control of the entire country during this period, large areas of China remained under the semi-autonomous rule of local warlords such as Feng Yuxiang and Yan Xishan, provincial military leaders, or warlord coalitions. Nationalist rule was strongest in the eastern regions around the capital Nanjing. The Central Plains War in 1930, the 