Complex sentence: The PCI moved away from communist orthodoxy since the late 1960s, when it opposed the Warsaw Pact invasion of Czechoslovakia and was one of the first parties to embrace Eurocommunism.
Split into simpler sentences: The PCI moved away from communist orthodoxy in the late 1960s, when it opposed the Warsaw Pact invasion of Czechoslovakia. In the 1970s, it was one of the first parties to embrace Eurocommunism.