Complex sentence: Stein now spent in retirement the months during which Napoleon completed the ruin of Prussia, but he saw Hardenberg called to office in April 1807 and important reforms effected in the cabinet system.
Split into simpler sentences: Stein now spent in retirement the months during which Napoleon completed the ruin of Prussia. Stein got to see Hardenberg called to office in April 1807 and important reforms effected in the cabinet system.