Complex sentence: Beck played a decisive role in early 1939 staunchly refusing Hitler's demands to subordinate Poland and turn it into a German puppet-state by giving away strategic territories in Pomerania to Germany and by joining the Anti-Comintern Pact directed against the Soviet Union.
Split into simpler sentences: Beck played a decisive role in early 1939, staunchly refusing Hitler's demands to subordinate Poland and turn it into a German puppet-state. Hitler demanded that Poland give away strategic territories to Germany and join the Anti-Comintern Pact directed against the Soviet Union.