Complex sentence: He took part as a second lieutenant in the 1944 Warsaw Uprising during the September campaign, first a soldier of the ZWZ (Związek Walki Zbrojnej), then the AK (Armia Krajowa).
Split into simpler sentences: He took part as a second lieutenant in the 1944 Warsaw Uprising. Participant of the September campaign, a soldier of the ZWZ (Związek Walki Zbrojnej), then AK (Armia Krajowa).