Complex sentence: Convinced by his own military service of the futility of the First World War, he supported Dawson's views in favour of appeasing Germany in the 1930s, though he switched to opposing further German expansion after the Germans invaded the remainder of Czechoslovakia in March 1939.
Split into simpler sentences: Convinced by his own military service of the futility of the First World War, he supported Dawson's views in favour of appeasing Germany in the 1930s. He switched to opposing further German expansion after the Germans invaded the remainder of Czechoslovakia in March 1939.