Complex sentence: In 1939, after Germany's occupation of Czechoslovakia, created and headed an underground organization Obrana národa ("Defence of the nation"), was under surveillance by the Gestapo, was a member of the underground Czechoslovak government, which served as minister of war.
Split into simpler sentences: In 1939, after Germany's occupation of Czechoslovakia, he created and headed an underground organization called Obrana národa ("Defence of the nation"). He was under surveillance by the Gestapo and was a member of the underground Czechoslovak government where he served as Minister of War.