Provinces of China
The Republic of China, established in 1912, set up four more provinces in Inner Mongolia and two provinces in historic Tibet, bringing the total to 28. In 1931, Ma Zhongying established Hexi in the northern parts of Gansu but the ROC never acknowledged the province. However, China lost four provinces with the establishment of the Japanese puppet state of Manchukuo in Manchuria. After the defeat of Japan in World War II in 1945, China re-incorporated Manchuria as 10 provinces, and assumed control of Taiwan as a province. As a result, the Republic of China in 1946 had 35 provinces. Although the Republic of China now only controls one province (Taiwan), and some islands of a second province (Fujian), it continues to formally claim all 35 provinces (including those that no longer form part of the area of the People's Republic of China).
The Battle of China
The introductory maps shown in the film show "China" as divided into "China Proper" and four outer provinces, namely "Manchuria", "Mongolia", "Sinkiang" (Xinjiang), and "Tibet". The very concept of a "China Proper"—either presently or historically—remains highly debated. The Japanese puppet state in Manchuria is discussed but never treated as actually separate from China. 
The borders of the outer territories follow the claims of the Republic of China, which means "Manchuria" includes some territory now administered by Russia and the film's "Mongolia" is Greater Mongolia, including the Qing and Republican province of Outer Mongolia (now the independent state of Mongolia) and including Tannu Uriankhai, now administered by Russia. Minor borderlands of Afghanistan, Pakistan, and India are also claimed, as well as large areas of the Tajik province of Gorno-Badakhshan, the Indian state of Arunachal Pradesh, and the Burmese state of Kachin.