Historians have interpreted the events at the Munich Conference, in which Britain and France essentially ceded the Sudetenland, and therefore Czechoslovakia, in many different ways. But the shortest way to answer this question is to point out what most historians agree on: Britain and France were desperate to avoid war with Germany, and the leaders of both nations, especially British Prime Minister Neville Chamberlain, thought that the concessions made at Munich would avert such a conflict. As Chamberlain said on his return to Britain after the Munich Conference, "the settlement of the Czechoslovak problem" was believed to be a "prelude to a larger settlement in which all Europe may find peace."
We see this pattern over and over after Hitler's rise to power. Both France and Britain had declined to act when Hitler militarized the Rhineland in contravention of the Versailles Treaty, when the Nazis openly supported Franco in the Spanish Civil War, and when Germany annexed Austria. This approach, of course, now appears disastrously wrong-headed and even craven and cowardly in retrospect, and indeed some leaders, most notably Winston Churchill, said so at the time. But historians have also emphasized several other factors. First, both France and Britain overestimated Germany's military might. Second, the United States, whose financial if not military arsenal would be crucial to any war against Germany, was unsupportive of firm action against Hitler throughout most of the 1930s. Finally, many in western Europe, while repelled by Hitler, saw Stalin and Communism as the greater threat. Hitler, while repellent to most in France and Britain, was a valuable strategic counterbalance. Again, we know now that the failure to resist Hitler early on was a factor that led to the outbreak of the war. But people did not know that at the time, and saw the strategy of appeasement pursued over the question of Czechoslovakia as a means of maintaining peace.