Why was the policy of appeasement in World War 2 significant?

Germany went from being a defeated country at the end of WW II, in 1918, to overrunning all of continental Europe in 1939, which was just 21 years later. The policy of appeasement, which was intended to make Germany happy so that it would not go to war, instead allowed Germany the opportunity to rebuild its military and to make all the necessary preparations for war, and to become the most powerful nation in Europe. So appeasement was a horribly foolish policy, as it turned out.