Blood, Toil, Tears, and Sweat by John Lukacs
The subtitle of this short book is "The Dire Warning: Churchill's First Speech as Prime Minister".  Churchill delivered this famous speech on May 13, 1940.  At the time, it was not at all clear if Britain could survive, it was not at all clear if Churchill was the right man to lead the nation, it was not at all clear if the British would stand alone, or fall alone, against the onslaught of Hitler's Germany.  Mr. Lukacs shows us why Churchill was the right man for the job:  he was one of the few who saw clearly what was at stake, the very survival of Western Civilization as it had been for over a thousand years.  Churchill did not know if the battle could be won; he only knew that it must be fought.  This is a stirring book, with resonance for our day.  I highly recommend it.