In the 1930's the world had just been hit with the Great Depression, with America being hit extremely hard. One of America's biggest bills was the massive amount of loans it had been giving to Germany for them to pay the reparations demanded of them in the Treaty of Versailles(1918). So when the Great Depression hit, America called in the debt and Germany had no hope of paying, it was simply impossible for them. The debt was massive, and they had to deal with both the Great Depression AND paying the Reparations. This, in the eyes of the American people, was a sign that Europe couldn't be depended on.