Complex sentence: Charles V left again to handle the advance of the Ottoman Turks, returning in 1547 to launch a military campaign against the Schmalkaldic League and to issue an imperial law requiring all Protestants to return to Catholic practices (with a few superficial concessions to Protestant practices).
Split into simpler sentences: Charles V left again to handle the advance of the Ottoman Turks. He returned in 1547 to launch a military campaign against the Schmalkaldic League and to issue an imperial law requiring all Protestants to return to Catholic practices (with a few superficial concessions to Protestant practices).