On March 16, 1935, Adolf Hitler announced that he would rearm Germany in violation of the Treaty of Versailles. Hitler revealed that Germany had begun to construct an air force, and unveiled plans to reinstitute conscription and create a German army of more than half a million men. Britain, France, Italy, and the League of Nations all issued statements condemning Hitler’s decision, but did little else to penalize Germany.

James M. Lindsay, CFR’s senior vice president and director of studies, notes that it was only on September 1, 1939, when Germany invaded Poland, that "the rest of Europe confronted, rather than appeased, Hitler." This four-year delay, he argues, points to a basic difficulty in international relations. "Aggressive, expansionist states are most easily stopped early on when they are weak and vulnerable," he says, but "precisely because their capabilities are limited at that point--and their intentions can only be guessed at--it is often hard to persuade other countries to act."

This video is part of Lessons Learned, a series dedicated to exploring historical events and examining their meaning in the context of foreign relations today.