Complex sentence: The Allied ground advance into Germany reached Mannheim in late March 1945, which was potentially well-defended by German forces, however, these suddenly abandoned the city and the U.S.44th Infantry Division entered unopposed on 29 March 1945.
Split into simpler sentences: The Allied ground advance into Germany reached Mannheim in late March 1945, which was potentially well-defended by German forces. However, these suddenly abandoned the city and the US 44th Infantry Division entered unopposed on 29 March 1945.