Answer: Because Chamberlain lost the confidence of the House of Commons
Explanation: Chamberlain was Prime Minister of Great Britain when World War II began. He had signed the Munich Pact with Hitler in 1938. But in September 1939 he had to declare war on Germany when they invaded Poland. Chamberlain lost the confidence of the House of Commons and resigned. Winston Churchill, First Lord of the Admiralty was called to replace him as Prime Minister.