The Book-of-the-Month Club selection for May, this vast, one-volume study of one of this country's foremost historians (authority on Christopher Columbus, official Historian of the U.S. Navy, etc.) breaks happily with convention, although superficially it follows accepted form. A social, political and military history of the United States, and also a boiled-down history of Canada, it begins normally enough with aborigines and early white settlers, continues through assorted wars, national development, slavery, westward expansion and similar matters, and ends in 1963 with the assassination of President Kennedy. In its treatment of this subject matter, however, the book deviates from tradition in several ways: its emphasis on the importance of American sea power (the chapter on Clipper ships is one of the best in the book); its inspired documentation; its comments on fiction, music, poetry and art in different periods of national development; and the gusto with which it is written. Dredging little-known facts from neglected sources, the 78-year-old author presents his own interpretation of the American past and his personal appraisal of this century's men and events. Giving balanced opinions of presidents and statesmen he has known, he writes bitterly of modern political corruption, blasts the influence of ""ad men"" on today's culture, and deplores the ""gaping holes torn in the country by expressways"" from which ""no home, no distinguished architecture of the past, no century-old trees by a quiet riverside"" are safe. Enormously readable in spite of its appalling length, this astonishing book presents a superb picture of the growth of this sprawling and magnificent continent, and belongs in all comprehensive collections of the annals of North America.