Complex sentence: Capitalizing on this opportunity, communists infiltrated Zeng's inner circle and convinced him to rebel against the nationalists and that was exactly what Zeng did after the pressure from the fall of Jinzhou.
Split into simpler sentences: Capitalizing on this opportunity, Communists infiltrated Zeng's inner circle and convinced him to rebel against the Nationalists. Zeng so did after the pressure from the fall of Jinzhou.