Several factors led to America adopting a policy of neutrality in the early 1930s. This included war debts from WWI, findings that arms manufacturers profited greatly from the war, and a rise in isolationism. The Neutrality Acts of the 1930s prohibited the sale of arms to countries at war and required warring nations to purchase supplies on a "cash and carry" basis. However, Hitler's aggression in Europe challenged this neutrality. He annexed Austria in 1938 and demanded territory from Czechoslovakia and Poland. When Germany invaded Poland in 1939, Britain and France declared war, beginning WWII.