Chamberlain was no war leader, but he should not be harshly criticized for Munich. At the time, Britain needed time to build up its Air Force, and war with Germany in 1938 over Czechoslovakia would have accomplished nothing. The UK and France were not in position to reinforce and supply Czechoslovakia.
If the UK and France had invaded Germany in 1938 as a means to relieve then Czechs, it would have meant that Britain would have had to expend more money and effort on the BEF land forces and less for air defenses. Although we will never know how things would have turned out, we do know that the outcome of the Battle of Britain was far from certain in 1940.
It should be noted that the Russians were a better geographic position to assist the Czechs, but of course no one ever blames Stalin.
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