Even by the norms of the British upper class, Churchill’s parents were neglectful. His politician father, Lord Randolph Churchill, treated Winston with cruelty and sarcasm when he noticed his son at all. His American mother Jennie was a glamorous society lady who shone–in Winston’s own poignant words–“like the evening star,” brightly but from a great distance. Like so many other young British patricians, he was saved from becoming a complete emotional cripple by a tender-hearted nanny.

The net result could have been predicted by any dabbler in psycho-analysis: The wartime prime minister carried around with him a keenly-felt need to win the approval of those he admired, and he was undeterred when the objects of his affection seemed cold or ungrateful. Churchill had several other childish qualities which on balance worked to his advantage. More than most products of the British private school system, he was in touch with his feelings: He was sentimental and easily moved to tears, but he also had a child’s ability to forgive and to seek forgiveness.

Roosevelt, by contrast, was showered with affection as a boy, as the adored only child of a 53-year-old father and a proud and ambitious 27-year-old mother. Secure, optimistic, and conscious of being more intelligent than average, he learned from an early age how to influence and, where necessary, to manipulate people. The president’s manipulative and at times devious quality was brought to the fore when he was stricken with polio and confined to a wheelchair; meetings and ceremonies had to be stage-managed even more carefully than before to compensate for his disability.

The contrasting, but in some ways complementary, personalities of Churchill and Roosevelt set the stage for a fascinating study of the importance–and limits–of one-to-one diplomacy at great moments in world affairs. Through hundreds of hours of elaborate ceremony, intimate conversation, shared recreation, and scores of affectionate hand-written notes, the two wartime leaders self-consciously cultivated their relationship. As Churchill himself said, with disarming frankness, “no lover ever studied the whims of his mistress as I did those of President Roosevelt.”

But the hard truth remains that all relationships, and in particular all political relationships, unfold in a context: They are determined not merely by the personalities involved, but by the external circumstances which make them more or less dependent on one another. From the very outbreak of the Second World War, Britain’s dependence on American help, whether direct or indirect, was acute, as Churchill could see more clearly than most of his compatriots.The United States, for its part, had a strong stake in Britain’s ability to keep Hitler at bay, but this was not self-evidently a matter of life or death for the American republic. Well before the Japanese attack on Pearl Harbor drew America into the war, Roosevelt was keen to help Churchill in any way that was politically feasible; but he was answerable to American public opinion, of which a large segment was isolationist, and to a political class which was by no means convinced of the complete identity of interest between the English-speaking powers. Hence the toughness of the terms on which America provided the British navy with destroyers; Roosevelt could not have helped Britain in purely a disinterested way, even if that was his dearest wish. But perhaps the most fundamental disparity between Britain and the United States is that the former had no alternative to the closest possible relationship with America, while for the United States, friendship with its former colonial master was only one option among many.

As the war raged on, and America’s vast manufacturing base progressively dwarfed that of Britain, the terms of the partnership changed in Roosevelt’s favor. Underneath all the bonhomie and protestations of friendship between the English-speaking peoples, Churchill was ever more conscious that the postwar world would be dominated by the two superpowers, America and Russia, with Britain struggling to maintain its place in the elite club. This inexorable reality, as well as the personalities involved, help to explain the bizarre drama which played out in November 1943 in Tehran, when the English-speaking leaders met for the first time with their ally, Joseph Stalin. Only weeks earlier, the prime minister had given a stirring address to Harvard University on the ties of “blood and history” that united the English-speaking democracies; and Churchill and his wife Clementine had spent their wedding anniversary being feted and toasted by the president at Hyde Park, his beloved residence on the Hudson River.

But in Tehran, Roosevelt went out of his way to snub Churchill; as part of a strategy to gain Stalin’s confidence, he refused to meet the prime minister alone, and insisted on having a private meeting with the Soviet leader, before they conferred as a threesome. Later, when Stalin needled and provoked Churchill, Roosevelt often seemed to take the Soviet tyrant’s side. In an especially odd scene, Stalin proposed the execution of 50,000 German officers-a joke apparently, but not a hilariously funny one from a leader who had already killed millions of his own subjects. Churchill stormed out of the room, his anger exacerbated by a burbling statement in support of Stalin from Roosevelt’s son, Elliott. Years afterwards, Churchill observed that he was never fully convinced that Stalin’s proposal was merely teasing.

In any overall assessment of the Churchill-Roosevelt friendship, these unhappy moments matter much less than the fact that in 1944, the two leaders jointly planned and oversaw the invasion of France, thus disproving Stalin’s charge that they were faint-hearted in their pursuit of war with Germany. D-Day was an operation in which tens of thousands of soldiers from both English-speaking democracies were bound to die-and one whose success was by no means guaranteed. Above all, it was a risk that Churchill and Roosevelt shouldered together. It is true, on one hand, that however great their mutual devotion, politicians from different countries cannot change the constraints-be they political, economic, or military–within which they have to act. They can test the limits of those constraints, however, by taking risks for one another; that, rather than fishing trips or drinking parties, is how real mutual trust can develop and have historic consequences. But friendship, and even trust, between leaders is never boundless. When Roosevelt died in April 1945, there was no reason to doubt the sincerity of Churchill’s grief; but the hard fact remains that Churchill decided, after considerable hesitation, to stay away from the funeral. Meacham reckons that Churchill was testing American friendship in the hope that the new president, Harry Truman, would pay an early state visit to Britain. That hope was disappointed.

Meacham, a managing editor at Newsweek and contributing editor of this magazine, is an excellent story-teller, with a fine talent for thumbnail sketches of people and scenes. On the whole, he lets the facts speak for themselves, and avoids veering off into speculation about the what-ifs of history, or about the importance of friendship as a factor in great events. In this tightly-packed but relatively short book, presented as a work of serious non-fiction (and, in the best sense, journalism) rather than academic scholarship, he has made the right choices. By focusing on a relationship, he will hold the attention both of non-specialists, and also of those enthusiasts who have pored through the hundreds of works previously written about the wartime leaders.

But there are at least two questions which are prompted but not answered by this book. First, were Churchill and Roosevelt so preoccupied by their own fraternal rivalry that they failed to understand Stalin, and therefore underestimated the cruelty with which he would treat the territories overrun by the Red Army? Of the two English-speaking leaders, it may be Churchill who had a better grip on Stalin’s ruthlessness; but the prime minister was certainly not averse to making geopolitical deals over the heads of small European nations. It was Churchill, after all, who proposed that the Soviet Union should have 90 percent of the influence in Poland, in return for allowing 90 percent British influence in Greece–much to the chagrin of Polish democrats and Greek communists. In any case, it could be argued that Roosevelt and Churchill might have restrained Stalin more successfully if Roosevelt had not been so preoccupied with the breaking up of Europe’s colonial possessions, including the British ones. Given that the British Empire was moribund anyway, was it ever worth making common cause, even rhetorically, with a tyrant like Stalin under the slogan of anti-imperialism?

The other question many readers of this book will ask is whether the Churchill-Roosevelt friendship has anything to teach us about the Anglo-American partnerships of modern times: Margaret Thatcher’s friendship with Ronald Reagan, and later George Bush senior-or Tony Blair’s interaction with Bill Clinton and now, George W. Bush.

The biggest change, of course, is the fact that over the past half-century, America’s relative power has grown and that of Britain has sharply diminished: It looks even more true now than in 1945 that if London wants a seat at the top world table, it has no real alternative to its Washington connection, while the American hyperpower has an almost infinite variety of choices.

From this point of view, it is easy to understand the thinking behind Blair’s pro-American foreign policy: Only by following the United States almost all the way can Britain hope to have some influence at the margins. During the 1990s, when a Tory government allowed quite serious differences with the Clinton administration to develop over Ireland and Bosnia, the end result was to Britain’s disadvantage; American presidents may be susceptible to nudging from close friends, but they do not take kindly to being lectured, as Blair’s predecessor John Major discovered.

Tony Blair may not have the historical vision or the animal charisma of a Winston Churchill; but he sensed from the outset that his relationships with White House incumbents must be made to work, and he has applied every drop of his personal skill to making friends with his American counterparts. But surely the main lesson from the Churchill-Roosevelt friendship is not about the scope of Anglo-American friendship, but about the constraints. However many steaks may be barbecued at the presidential ranch, the United States and Britain have different (albeit heavily overlapping) interests, and above all, different electorates, as Tony Blair is now discovering.

Earlier this year, many British voters were open to persuasion that war against Iraq was a just cause, as long as all the available facts had been gathered and considered in good faith. But they will not forgive their prime minister if it becomes obvious that “his” decision to join the war had, in fact, been made in Washington at least a year beforehand-and all subsequent discussions of the threat posed by Saddam Hussein were simply going through the motions. British citizens are neither viscerally anti-American, nor indifferent to the spread of non-conventional weapons-but they will not pardon a prime minister who pretends to be wrestling with an unresolved dilemma when, in fact, his hands have been tied by a decision made much earlier. More than once, Blair assured British voters that he had made no decision to go to war. But the investigation following the suicide of weapons expert David Kelly makes clear that preparations for war actually began last year. For all his flexibility, intelligence, and flair, this may yet be Blair’s downfall. A calculated risk-taker by temperament, he may have taken one risk too many, in the cause of friendship with George W. Bush.

How does this compare with Churchill and Roosevelt? Beneath all the ostentatious (and doubtless, sincere) affection which they heaped on one another, the wartime leaders never forgot that their nations were in different places, geographically, historically, and even psychologically. The United States was on the brink of its emergence as an unmatched global power, while the British Empire, underneath all the pomp and pageantry, was living out its final years. It is a mark of both leaders’ greatness that they understood how broadly their countries’ interests coincided, and also where they diverged. As Meacham’s excellent book reminds us, there is no such thing–in international politics, any more than in domestic politics–as unconditional friendship. As Harry Truman once said, only dogs can offer that.