The two men had not seen each other since and in the 1930s appeared to be polar opposites. Roosevelt was the charismatic president, Churchill the has-been stuck in the political wilderness; Roosevelt the scourge of European colonialism, Churchill the die-hard defender of the British Empire. But one thing united them. They had both understood from early on that Hitler presented a new and terrible force with which peaceful co-existence would be impossible.

There had been a coincidence in Roosevelt’s and Hitler’s rises to power. On March 4, 1933, Roosevelt was inaugurated as president for the first time. The next day Hitler tightened his grip on the German nation after a slim but sufficient win at the polls. But it was not until three years later, when German troops marched into the Rhineland on March 7, 1936, that Roosevelt’s anxieties crystallized. The United States was a neutral country; its people wanted no entanglements in Europe’s squabbles. Roosevelt could only express his fears in private. One important confidante was his distant cousin and close companion, Daisy Suckley. He wrote to her: "The news from Germany is bad and though my official people all tell me there is no danger of actual war I always remember their saying all the same things in July 1914."

The president could only watch as Hitler’s onward march trampled through the enfeebled leaders of Britain and France. In March 1938 he told a colleague: "As someone remarked to me—‘If a Chief of Police makes a deal with the leading gangsters and the deal results in no more hold-ups, that Chief of Police will be called a great man—but if the gangsters do not live up to their word the Chief of Police will go to jail.’ Some people are, I think, taking very long chances." After a speech by Hitler at the height of the Munich crisis in September Roosevelt conveyed to Suckley his visceral contempt for the Nazi leaders: "Did you hear Hitler today, his shrieks, his histrionics, and the effect on the huge audience? They did not applaud—they made noises like animals."

When Churchill returned to the British Cabinet as First Lord of the Admiralty on the outbreak of war, Roosevelt immediately understood that he would become an important protagonist in resisting the Nazis and started a transatlantic cable correspondence with him. In his first message he wrote: "My dear Churchill, it is because you and I occupied similar positions in the World War that I want you to know how glad I am that you are back again in the Admiralty." Privately Roosevelt told the American ambassador to Britain, Joseph Kennedy: "I have always disliked him since the time I went to England in 1918. … I’m giving him attention now because there is a strong possibility that he will become Prime Minister and I want to get my hand in now." On May 10, 1940, Roosevelt’s forecast was vindicated.

On the other side of the globe, the world’s fourth great leader was also taking stock of the cataclysm of May 10. In Moscow Hitler’s collaborator, Joseph Stalin, dutifully dispatched his deputy, Vyacheslav Molotov, to the German embassy with a personal message for the Führer. "He realised that Germany must protect herself against British-French attack," the ambassador, Count von der Schulenburg, reported back to Hitler, "he had no doubt of our success." These honeyed words of congratulation from one ally to another were a front; obligatory praise that masked a deep anxiety. The truth was that Stalin and Hitler, though neither of them yet fully realized it, were nine months into a psychological duel that would have devastating consequences for themselves, their nations and the world.

It had been instigated the previous summer by Hitler. During July 1939 the world’s most celebrated Wagner fan attended no fewer than seven performances of his favorite composer and then retreated to spend the balmy days of high summer at his mountain retreat, the Berghof in Obersalzberg. Encamped in one of the world’s loveliest places, Hitler planned the brutal invasion of Poland, his "little war" as he called it and one that he was determined to have. The urge for war had been building ever since the Munich agreement the year before, when, rather than being pleased by British and French appeasement over Czechoslovakia, Hitler had felt deprived of the chance to flex his military muscles.

Reprinted from Warlords, Copyright 2006. Reprinted by permission of Da Capo Press.