Complex sentence: To some extent he followed policies later known as appeasement, believing that that the League of Nations Was the key to preventing the next war, and tried to enlist the French in efforts to get the Germans to cooperate.
Split into simpler sentences: To some extent, he followed policies later known as appeasement, as he believed that that the League of Nations was the key to preventing the next war. He tried to enlist the French in efforts to get the Germans to cooperate.