The magnitude of their victory [in France] deceived the Germans. It seemed impossible that the British would consider further resistance. In fact, the change from Chamberlain to Churchill had created a very different atmosphere in London.
Churchill brought extraordinary leadership to the struggle... He nobly gambled the last resources of a fading empire in the belief that the struggle was not yet lost. He was right.
(A War to Be Won)
Seventy years later and it is still frightening to ponder the "what ifs" of 1940. How does our world look today if Churchill is not PM in June 1940? What if Britain follows Halifax's advice to make peace and "save the country from avoidable disaster"?