H.W. Brands, author of “The Man Who Saved the Union: Ulysses Grant in War and Peace,” speaks free of charge at 7:15 p.m. Tuesday, Oct. 16, at the Georgia Center for the Book in the Decatur Library, 215 Sycamore St., Decatur. 404-370-8450, www.georgiacenterforthebook.org.

Was Ulysses S. Grant a drunk?

Not really, concludes Pulitzer-nominated historian H.W. Brands, who speaks Tuesday at the Georgia Center for the Book, in the Decatur Library.

Brands is the author of “The Man Who Saved the Union: Ulysses Grant in War and Peace,” a new, formidable biography of a devastatingly effective general and an underrated president.

“Grant’s problem was not that he drank too much, but he couldn’t hold his liquor,” said Brands, a professor of history at the University of Texas, in a conversation from his home in Austin.

Grant’s most notorious bender occurred in 1854, as a young officer stationed at Fort Humboldt in rainy northern California. He had already served in the Mexican War, was thousands of miles from home, hadn’t seen his wife in months, didn’t like the weather, was undoubtedly depressed, and was surrounded by veterans who, in peacetime, had nothing to do but tipple. Grant couldn’t keep up.

“One glass would show on him,” said a fellow officer, “and two or three would make him stupid.”

After being discovered inebriated at his post, he resigned rather than face charges.

The blot on his career would dog him, though not derail him. “He didn’t know he’d be back in the military, and that the Army never forgets,” Brands said. Other officers, alarmed at Grant’s meteoric rise after he re-enlisted during the Civil War, tried to torpedo his career. To no avail.

“I never could cite a time when Grant’s drinking at all interfered with his ability to lead the Army during the war or during his presidency,” Brands said.

During the war, in particular, Grant was one of those creatures who thrived. Though he was mediocre at business, he found his niche in combat and became President Abraham Lincoln’s favorite: “He makes things git!” the commander in chief said.

Unafraid in battle, Grant was able to inspire courage in others. “Grant discovered early on when everyone was getting crazy, he became calmer,” Brands said.

He was also a consummate strategist. Grant was not just a student of military history but had a preternatural ability to visualize the battlefield and anticipate the enemy. As a former quartermaster, he knew the importance of delivering the bacon and the bullets to the troops in the field.

Every scholar of American history must deal with the Civil War as a central event in the creation of the country, and until this year, Brands had skirted the issue.

His work, a chain of linked biographies, began with founding father Benjamin Franklin and then skipped into the modern era with the Roosevelts, Theodore and Franklin.

He knew he would, eventually, tell the story of the war using a single central figure. “People’s eyes glaze over when you talk about history, but people will buy and read biographies.”

Grant’s life ideally bridged the era before and after the war.

“From the standpoint of American history, you can’t stop at the end of the Civil War,” Brands said. “That’s when things get complicated and, in many ways, more interesting.” As president, Grant fought the Ku Klux Klan, tried to protect the Plains Indians and vigorously pursued the policies that actually enfranchised black Americans.

Much of his effort was undone after his death, and historians criticized his presidency, writing off Reconstruction as a period of corruption. Because his political enemies wrote the history of Reconstruction, Brands said, this version of events remained unchallenged for the next hundred years.

Brands doesn’t argue that Grant was a great president, just a good one, a man of no great ambition who was in the right place at the right time, and tried to do the right thing.