What explains the dominance of America and Britain in global affairs over the past three centuries? How have these states maintained this top-dog position in the face of so many challengers over the years? These questions have been tackled by many historians, and the usual answer provided is that these two nations managed to combine technological innovation, financial resources, and a seaborne global trading network into something close to a self-sustaining wealth machine. For both of these states, trade kept the coffers full at home, and these riches allowed for further technological advances, while technology underpinned military strength and allowed for the projection of global power. When Britain or America went to war with continental European or Asian rivals, they were able to draw upon this strategic and industrial base to sustain themselves, coming out the victors time and again.

Walter Russell Mead, the Henry A. Kissinger Senior Fellow in U.S. Foreign Policy at the Council on Foreign Relations, accepts these explanations, but in his new “God and Gold” (Alfred A. Knopf, 450 pages, $27.95), he adds one more: culture. In his study, he emphasizes that Anglo-American ascendancy in world affairs is inextricably linked to culture and religion. The English-speaking peoples, he argues, believe in individual ambition, have become fierce advocates of democracy, and share a common Protestant ethic that promotes economic well-being. Americans today have faith — literally — in the invisible hand of capitalism, Mr. Mead says. Our confidence, our religious zeal, and our success have made us unpopular in the world, but we have hit on a winning formula. Adding God to gold and gunboats has led British and American leaders, as well as the nations they represent, to believe that their industrial and military might comes with a heavenly seal of approval.

Mr. Mead’s book is a welcome contribution, since historians of grand strategy are notoriously tone-deaf to the question of culture and the role it plays in the making of national power. The book probably could have made this argument a bit more nimbly, however: One has to plow through lengthy digressions into Jonathan Swift and Immanuel Kant, Lewis Carroll and Daniel Defoe, Henri Bergson and Karl Popper, Cromwell, President Reagan, the Cold War, and a wealth of other topics to grab the essentials of the argument. There is also a jocular tone that runs through many parts of the book that seems out of place in a work of such scale and ambition. For example, Mr. Mead suggests that British and American elites subscribe to something he calls the “Protocols of the Elders of Greenwich” — a kind of rule book for Anglo-American WASP dominance, and a tasteless reference to the anti-Semitic tract, “Protocols of the Elders of Zion.”

A more substantial objection is that Mr. Mead’s emphasis on a cultural explanation for Anglo-American power leads him to downplay the importance of economic, technological, and military power over the long run. In his last section, titled “The Lessons of History,” Mr. Mead seems remarkably complacent about the future ability of America to sustain itself in the face of global challengers. He suggests that what has been will continue to be: American global dominance will, in all likelihood, continue because of the religious, cultural, and social dynamism of the nation. The forces of history are on our side, he suggests, and we will repel ideologues, Muslim fanatics, Iranian missiles, and global warming with the same aplomb that Cromwell employed to dispatch the royalists. “The plan works,” he concludes. “Stick to the plan. The ‘protocols of the elders of Greenwich’ are still the best guide to grand strategy.”

Surely, American democratic values and the Protestant work ethic are valuable assets. But are they enough to offset China’s rapid industrialization, Russia’s drift toward authoritarian rule, America’s titanic trade deficits, a weakening dollar, spiraling oil costs, the proliferation of nuclear weapons, and of course Islamic fundamentalism and the terror it has sown? Mr. Mead suggests we take the longer view, and not fret too much about these matters. That seems a dubious prescription for American foreign relations in the 21st century.

Mr. Mead tells us that while researching this volume, he could not find “any recent books that address the whole subject [of Anglo-American power] in a serious way.” But there are a few works that should be read alongside Mr. Mead’s book, such as William H. McNeill’s elegant, prize-winning “Rise of the West” and Paul Kennedy’s “The Rise and Fall of the Great Powers.” These works suggest that throughout history, empires and civilizations have had an organic quality to them: They rise and fall in remarkably predictable patterns. Furthermore, they are rarely good at seeing around the corner, and anticipating the great body blow that will push them off their perch. Indeed, when your experts tell you that your empire will last forever, that is probably the very moment to start worrying.

Mr. Hitchcock teaches history at Temple University. His book, “Liberation: Europeans, Americans and the Recovery of Freedom at the Close of World War II,” will be published by the Free Press next year.