Complex sentence: The direct pretext for Operation Wisła was the March 28,1947, assassination of the Polish communist General Karol Świerczewski in the ambush had allegedly been set by the UIA's "Chrin" and "Stach" "sotnias".
Split into simpler sentences: The direct pretext for Operation Wisła was the March 28,1947, assassination of Poland's General Karol Świerczewski. The ambush had allegedly been set by the UIA's "Chrin" and "Stach" "sotnias".