 Strzembosz was one of the few Polish People's Republic historians who refused to write Soviet-inspired falsehoods about Poland's history.His main areas of research included the history of the World War II Polish Underground State, with special emphasis on German-occupied Warsaw; the Polish partisan movement in the "Kresy" macroregion between 1939 and 1941, following the Soviet invasion of Poland; and the 1944–46 anti-communist resistance in Poland.In the 1980s Strzembosz was an activist in the anti-communist Solidarity movement.