Hendrik Willem van Loon visited Germany lots of times in the 1920s. In 1933, when the Nazis ruled Germany, they told him he could not visit Germany any more. In 1938, Hendrik wrote a book that he called "Our Battle: Being One Man's Answer to "My Battle" by Adolf Hitler". This book said why Hendrik did not like Adolf Hitler's book "Mein Kampf". ("Mein Kampf" means "My Battle" in the German language.) Franklin Delano Roosevelt liked Hendrik's book "Our Battle" very much. In 1940, Hendrik helped Roosevelt try to get to be President of the United States.