"Appeasement" usually refers to the Munich Pact, an agreement signed with Adolph Hitler in September, 1938. It was intended to keep Europe at peace. But appeasement of aggressive regimes does not tend to produce peace.
Germany under Hitler began taking over neighboring territories. At first other international powers were not ready to do anything to stop German expansion. After the German occupation of the Rhineland (1936), incorporation of Austria (1938) and occupation of Sudetenland, the British and French prime ministers signed a pact with Hitler at Munich (September, 1938), which essentially gave him control over Czechoslovakia. They thought Hitler would stop there, but he didn't. A year later the Germans invaded Poland, which marked the beginning of World War II in Europe.