The Germans hated the Treaty of Versailles and throughout the 1920s and 1930s her politicians tried to reverse the terms of the treaty. In the 1920s Hitler and the Nazis gained support as they promised to reverse the treaty. In the 1930s when the Nazis were in power, Hitler set about reversing these terms. Britain believed that Hitler should be allowed to do this and this policy of letting the Germans take back their lands and building their armed services was called Appeasement.
Britain also appeased Italy and Japan. Italy joined Britain and France in 1915 after territorial gains were promised to the Italians if they fought against the Germans. In 1919 Italy gained very little and felt snubbed.
Japan had fought alongside Britain in the First World War but was snubbed by the Great Powers in 1919. Both Italy and Japan faced economic problems in the 1920s and were dominated by right-wing extreme governments. To solve their problems both countries set about creating empires. Britain and France let them get away with this as they were not prepared to start a major war. This was appeasement.