H.W. Brands’s book Reagan: The Life, to be published in May by Doubleday, is the capstone of a series that took a dramatic turn from the author’s original intention (indeed, capstone seems to be the only word for a book weighing in at 800-plus pages).

Brands, who spoke to me from his home in Austin, Tex., recalls: “I had this grand plan for writing the history of the United States in six volumes. This was in the mid-1990s; I was fairly young and very ambitious. I pitched it to a publisher, who just laughed at me. ‘You’re crazy,’ the publisher said. ‘Nobody writes that kind of history anymore, and nobody would read it if you wrote it.’ I was briefly discouraged, but I still thought it was a good idea, because I liked the idea of telling this great big story in several volumes.”

Brands realized then that he had pitched it the wrong way. “People are interested in people,” he says. “They buy biographies; they don’t buy studies of presidencies. What I could do was tell this story in the form of a series of biographies. I didn’t initially intend that they would nearly all be presidential biographies, but I discovered that presidents are peculiarly good at allowing the biographer to tell the story of the times, because presidents are right in the thick of the big events.”

About 20 years have passed since Brands began the six-volume series, which covers the lives and times of Benjamin Franklin, Andrew Jackson, Ulysses S. Grant, Theodore Roosevelt, Franklin Roosevelt, and Ronald Reagan. During those same two decades, he wrote a dozen other books, on topics ranging from the war for Texan independence (Lone Star Nation, 2004) to Gilded Age crime (The Murder of Jim Fisk for the Love of Josie Mansfield, 2011); Brands also held down a full professorship with teaching responsibilities, first at Texas A&M and then, starting in 2005, at the University of Texas at Austin. Even for someone as energetic and focused as the 61-year-old Brands, it seems a staggering amount of work.

Brands says that his teaching, research, and writing complement one another, with teaching giving him a head start on his writing projects. “When I wrote about Franklin Roosevelt [Traitor to His Class, 2008],” he says, “I had been teaching about him for 25 years, so I didn’t have to do a lot of background research. Also, when you teach you are in essence composing your thoughts in a way that conduces to writing for a general audience, because you’re explaining things to people who don’t know about them.”

“The other thing,” Brands adds with a grin, “is that when I’m writing I can try out my ideas on my students. While I was working on Reagan, every time I needed an example of some aspect of American politics or presidential leadership, my examples were inevitably drawn from Reagan; when I was writing about Franklin Roosevelt, my examples were a lot more about him!”

Brands sees these two very different presidents as “the bookends of the American century.” He says: “When you look at the development of the American presidency, you see that the presidents who have had the greatest impact are the ones who fit their times most successfully. Then you see how Reagan really is very much like Roosevelt, who came along at a time when the private sector was in disarray; American capitalism and business seemed to be on their last legs, so Americans looked to government for solutions to the problem. Roosevelt, being inclined in that direction, was just the person to be president then. By the time Reagan came along, liberalism seemed to have gone too far; most Americans had decided by the 1970s that maybe looking to the government to solve America’s problems wasn’t getting the results they wanted. Reagan legitimized the questioning of any government program; since him, there have been very few important new federal programs, and those very few have come with great difficulty.”

Just as Reagan and Roosevelt are more alike than it would seem, Brands believes the swings in American public opinion from liberalism to conservatism are often overstated. “This is always just a marginal shift. When F.D.R. was president, Americans were in a liberal mood, but there was still probably 40% of the country who were staunch conservatives. Reagan won reelection in 1984 with nearly 60% of the vote, so one could say that 60% of Americans were in favor of a conservative approach, but there were still 40% who liked the old liberal ideas. What we see is a pendulum that doesn’t really swing very far; it just oscillates back and forth in a fairly narrow range.”

Today’s Tea Party conservatives, Brands says, have ignored the lesson their idol learned from that electoral reality: “Reagan, as a practicing politician, was much more flexible and pragmatic than his speeches, which expressed a 100%-consistent conservative line, would lead you to believe. Reagan understood that the point of getting elected was to govern, to make progress, not just to score rhetorical points. He knew that politics is compromise. I quote James Baker in my book, who said that Reagan told him repeatedly, ‘I would rather get 80% of what I want than go over the cliff with my flag flying.’ ”

Although Brands has written about political issues for more than a quarter century, he’s conscious that they are not the only—or even the most important—strands of American history. “Politics is not something most people have to do every day,” he says. “Their daily lives are much more influenced by job opportunities, whether the country is in a recession or a boom period. If you really want to understand what drives American history, look at the economic... side.”

Brands has explored this idea in such books as [em]Masters of Enterprise[/em] (1999), American Colossus (2010), and Greenback Planet (2011). “I have a personal interest, because I grew up in a family business: my grandfather, then my father, and now my brother imported and wholesaled knives and scissors. I didn’t choose it as a career, but I find business very interesting. There’s hardly a more fascinating cast of characters than the people who’ve built the American economy.”

Nonetheless, it’s back to politics for Brands’s next book, a study of the conflict between President Harry Truman and Gen. Douglas MacArthur over the conduct of the Korean War.

“I decided I needed a break from biography per se,” Brands explains. “Some stories in history lend themselves to being told in biographical form. I think of them as being long and narrow—windows on the past, the width and length of a person’s life. But there are other stories that focus on lots of people over a short space of time, like my history of the California gold rush (The Age of Gold, 2002). This new book allows me to look at Truman and MacArthur, not through their whole lives, but just at this moment when the interaction between them really crystallizes much larger forces. I’m drawn to the interplay between individuals, and how that intersects with history; it’s the link between what I sometimes call the little history of individual lives and the big history of nations.”

Wendy Smith is a contributing editor at the American Scholar and reviews books for the Washington Post, the Boston Globe, the Los Angeles Times, and the Daily Beast.