Complex sentence: The 165th, 201st and 271st Regiments formed the 3rd Infantry Division, while the 2nd, 141st and 209th Regiments formed the 7th Division.
Split into simpler sentences: The 165th, 201st and 271st Regiments formed the 3rd Infantry Division. While the 2nd, 141st and 209th Regiments formed the 7th Division.