Complex sentence: In 1968 CPFI (and) FPDL were the only parties to directly oppose the actions of the Soviet militarship in Prague in 1968, thus the two organizations split "de facto" into two different parties, one reformist and one hard-line Soviet.
Split into simpler sentences: In 1968 CPFI (and) FPDL were the only parties to directly oppose the actions of the Soviet militarship in Prague in 1968. Thus, the two organizations split de facto into two different parties, one reformist and one hard-line Soviet.