Complex sentence: Repeated bombing of Bremen in World War II resulted in the mass-production plants being moved to eastern Germany and Poland, using many foreign and forced labourers, and from 1944 also prisoners of war.
Split into simpler sentences: Repeated bombing of Bremen in World War II resulted in the mass-production plants being moved to eastern Germany and Poland. Those plants used many foreign and forced labourers, and from 1944 also prisoners of war.