Was appeasement a failure?
Appeasement was a complete failure. It did not in any way do what it was supposed to.
Appeasement was supposed to stop Hitler from wanting to take more of Europe. The French and the British let him have the Sudetenland on the understanding that he would not ask for anything more. By doing this, they thought they were preventing a war and ensuring that Hitler would not take any further territory in Europe.
Of course, neither of these things happened. Hitler went on to take all of Czechoslovakia and then to invade Poland. This started WWII. Clearly, then, appeasement did not prevent the war or prevent Hitler from trying to take more territory.