Roberts offers an outstanding example of a joint biography in this study of the actions and interactions of Franklin Roosevelt, Winston Churchill, George Marshall and Alan Brooke. The president, the prime minister and their respective army chiefs of staff were the vital nexus of the Anglo-American alliance in WWII. The path was anything but smooth. London-based historian Roberts (A History of the English-Speaking Peoples Since 1900 ) demonstrates his usual mastery of archival and printed sources to show how the tensions and differences among these four strong-willed men shaped policy within a general context of consensus. The politicians had to master strategy; the soldiers had to become political. The result was “a complicated minuet.” The increasing shift of power in America's direction coincided with the achievement of the central war aims agreed on for the Mediterranean and with the viability of a cross-channel attack. Last-minute compromises continued to shape grand strategy, a good example being the choice of Dwight Eisenhower over Brooke to command Operation Overlord. Flexibility and honesty, Roberts concludes, enabled focus on a common purpose and established the matrix of the postwar Atlantic world. 16 pages of b&w photos, 7 maps.