After all, Germany needed to defend itself against Communist Russia.
There was a growing fear of Communism in Europe and was regarded as a threat by all other European countries. As far as Britain and France were concerned, a strong Germany could help save Europe from the spread of Communism. .
Chamberlain knew that without any support from powerful countries such as USA and USSR, war with Germany would be very risky. .
The USSR were In 1937, Stalin executed almost all his military leadership. This weakened the fighting capacity of the Russians.
At that time, America was isolationists because it had been devastated by the Depression and they needed to rebuild their own country. They were not interested in the events in Europe. President Roosevelt said "we shun political commitments which might entangle us in foreign wars". In 1937, a Neutrality Act was passed in. Furthermore, the USA only spent 1.5% of its national income on defense, while Germany spent 23.5% in the same year. As a result, America could no help America in any struggle with Germany.
Hitler had strong weapons, as seen in the Spanish Civil War, and many countries would not be able to compete with his weapons. Neither Britain nor France was fully ready for war in 1938, so appeasement gave them time to rearm: Britain introduced their four-year rearmament plan and France was building its defensive Maginont Line. While they were rearming, so was Hitler. By Munich, Chamberlain did not think that Britain should risk a war, and his military advisers "urged him to play for time". From these factors we could see that Chamberlain was reasonable and appeasement seemed very sensible at the time. Hitler misled Chamberlain. Hitler lied over and over again, but the British didn't seem to see through him. .
In contrast, it is hard to ignore many things that could have been done instead of simply giving in to Hitler. Chamberlain should have easily seen through Hitler's lies.