Complex sentence: Following a Japanese invasion in the 1940s, the First Indochina War eventually led to the expulsion of the French in 1954, leaving Vietnam divided politically into two states, North and South Vietnam.
Split into simpler sentences: Following a Japanese occupation in the 1940s, the Vietnamese fought French rule in the First Indochina War, eventually expelling the French in 1954. Thereafter, Vietnam was divided politically into two rival states, North and South Vietnam.