Complex sentence: The dispute and ambiguity over which "China" resulted from the Republic of China's loss of its mainland territory in the Chinese Civil War to the Chinese Communists in 1949, when the Communists established the "People's Republic of China" on that territory.
Split into simpler sentences: The dispute and ambiguity over the meaning of "China" and which "China" stemmed from the division of Republic of China into two Chinas in the Chinese Civil War in 1949. The Chinese Communists eventually won control of most of ROC's territory (mainland China) in 1949, when they proclaimed the "People's Republic of China" on that territory.