Why did Britain and France begin and end their policies of appeasement?

Before World War II began, Great Britain and France used the policy of appeasement. Since the early 1930s, there had been a lot of aggressive actions in Europe and in Asia. Japan had invaded Manchuria and part of China while Italy occupied Ethiopia. Germany moved its military into the Rhineland, had taken over Austria, and wanted to take control of the Sudetenland. Great Britain and France wanted to meet with Hitler and Mussolini about Germany's demand to take over the Sudetenland. Neither Great Britain nor France wanted war, and the leaders of these countries hoped that they could reach an agreement to prevent another war. As a result, the Munich Pact was made, in which Germany got control of the Sudetenland while agreeing to take no more land. The leaders of Great Britain and France truly believed that this agreement had saved the world from another war.
Great Britain and France abandoned this policy when Hitler broke the agreement by taking the rest of Czechoslovakia in 1939. It was clear that Hitler had manipulated the British and French leaders. These leaders made it clear that any additional aggressive actions would lead to war. The German invasion of Poland in September 1939 led to the start of World War II.
https://www.history.com/this-day-in-history/munich-pact-signed