Complex sentence: In 1941 Jürgens participated in Operation Barbarossa the invasion of the Soviet Union the 4th SS Polizei Division was attached to Army Group North which advanced through the Baltic States towards Leningrad.
Split into simpler sentences: In 1941 Jürgens participated in Operation Barbarossa the invasion of the Soviet Union. The 4th SS Polizei Division was attached to Army Group North which advanced through the Baltic States towards Leningrad.