Walter McDougall’s horizons are narrowing. His 1985 Pulitzer Prize winner, The Heavens and the Earth, took for its field of view the universe, or at least that part of outer space in which the United States and the Soviets conducted their Cold War race. His 1993 Let the Sea Make a Noise spanned the largest ocean on earth, covering half a millennium of the history of the Pacific Ocean and the countries that border it. Since 2004, when Freedom Just Around the Corner appeared, McDougall has confined himself to North America and particularly to that portion of the continent which became the United States.

His current book, Throes of Democracy, is the sequel to Freedom Just Around the Corner, and the second volume in a projected trilogy on American history. Not many historians would attempt such a project single-handed; it’s the sort of thing academics typically undertake in teams. But McDougall, a professor at the University of Pennsylvania, prefers his own company, and that independent streak shows in the audacity of his work. He ranges broadly over his merely continental-sized field, covering aspects of social history, economic history, literary history, immigration history, and assorted histories of science, technology, race and gender. He parses the language of Irish immigrants, ascribing the passivity of their sentence structures to a fatalism bred of centuries of English oppression. He recounts the rise of the circus in America, explaining that while P.T. Barnum did not coin the phrase “There’s a sucker born every minute”—McDougall credits Chicago gambler Mike McDonald—the circus impresario exploited its underlying truth better than just about anyone else.

McDougall’s prose can be masterly. His depiction of the fire that ravaged New York in 1835 recalls the human horror of the disaster, even while letting McDougall delineate the emergence of the new capital of American commerce and the broader economic transformation it portended. His biographical sketches are vivid: Mormon founder Joseph Smith was “simultaneously an eminent Jacksonian, a scion of the Yankee exodus”—from New England—“a creature and critic of the Second Great Awakening, a Romantic reformer, a charismatic utopian, a mystic nationalist, and a hustler in the manner of Barnum.” McDougall pries beneath standard interpretations to reveal forgotten aspects of everyday life. “What most people don’t know is how well the train whistle harmonized with the whinny”, he observes of the dawn of the railroad era, pointing out that the iron horse, far from putting real horses to pasture, actually increased the demands upon the latter. “Freight and passenger cars, after all, were confined to their rails. So...