Complex sentence: There was military invasion from 1977--78 by Pol Pot and the Khmer Rouge army and almost all of the people in An Phu had to be evacuated (mainly to the Cho Moi, Phu Tan district).
Split into simpler sentences: There was military invasion from 1977--78 by Pol Pot and the Khmer Rouge army. Almost all of the people in An Phu had to be evacuated (mainly to the Cho Moi, Phu Tan district).