Why did war break out in september 1939?

After signing the Munich agreement people thought appeasement worked but in March 1939 Hitler betrayed France and Britain and ordered his armies to occupy Bohemia and Moravia, two parts of Czechoslovakia. It then became a 'Puppet state' which was ruled by Germnay. On March 23rd Hitler also siezed memel from Lithuania. This showed that Hitler couldn't be trusted, Chamberlain was furious at Hitlers betrayle and Hitlers arguement for 'Greater Germany' was no long viable.

Britain and France both wanted to protect Polland from Nazi Germany and stop Germany growing stronger. They both sped-up rearmament and garuanteed to defend the independence of Polland.

The Nazi-Soviet…