Chongqing is the largest and most populous of the People's Republic of China's four provincial-level municipalities, and the only one in the less densely populated western region of China. Chongqing was also a municipality of the old Republic of China. Its abbreviated name is derived from the old name of a part of the Jialing River that runs through Chongqing and feeds the Yangtze River. As the provisional Capital of China for almost ten years (1937 to 1945), it was also known as one of the three headquarters of the Allies. Chongqing has many historical World War II buildings or sites.