Complex sentence: Bokor Hill was abandoned first by the French in late 1940s, during the First Indochina War, because of local insurrections guided by the Khmer Issarak, and then for good in 1972, as Khmer Rouge took over the area.
Split into simpler sentences: Bokor Hill was abandoned first by the French in late 1940s, during the First Indochina War, because of local insurrections guided by the Khmer Issarak. The Bokor mountain is abandoned again in 1972, as Khmer Rouge took over the area.