It's true that appeasement doesn't look like good. In fact, it had lots of disadvantages which looked very huge. At first, it made Hitler stronger. Through appeasement, Hitler had lots of lands and confidence he can do anything. For example, when Germany invaded the Rhineland and Austria, Britain and France did nothing. They believed if they returned the land which Germany was lost by Treaty of Versaille, Hitler will satisfy and be harmony with other European countries, so they even did Munich agreement and gave Hitler Sudetenland. Maybe it will give Hitler confidence which he can do anything and Britain and France are afraid of Germany. It also made more German Nazi (through the Germans in Sudetenland and Danzig.) which supported Hitler and more German territory for war. The second, through appeasement, no one trusted Britain, because there were many affairs which Britain couldn't keep their promises. For example, When Britain did appeasement, chamberlain said Germany surely won't make a war and he persuaded Czechoslovakia to give Sudetenland to Germany. (Actually, Czechoslovakia wanted to protect it) But he was completely wrong! Czechoslovakia lost Sudetenland and Hitler wanted more and more and finally invaded the Czechoslovakia which don't relate to Germany. (I mean in Treaty of Versaille.) No one trusted Britain.
Until now on,