It was a picture-perfect late-summer morning, the sky like blue glass, never hinting at the shattered lives to come. Christine Heyrman’s husband was sitting at his desk at the Pentagon, reviewing defense contracts, on what started out as a typical day at work. At 9:37 a.m., terrorists crashed American Airlines Flight 77 into the building, just three corridors away from his office. The impact sent him flying in his office chair on wheels.

“He called me in his best John Wayne voice to tell me they were having ‘a little excitement’ there,” says Heyrman, the Robert W. and Shirley P. Grimble Professor of American History at the University of Delaware. “He had found a working phone in a nearby Chinese restaurant and told me he was OK. I never felt so thankful in my life.”

In the aftermath of the 9/11 attacks, in grieving the thousands of lives taken and families forever changed, Heyrman also became increasingly concerned by the outpouring of hate toward Muslims and their faith.

“I saw it as a betrayal of the principles of this country,” she says.

That’s when Heyrman resolved to uncover the origins of American attitudes toward the Middle East. The 15-year journey took her to libraries in New England to Syria, Turkey, Egypt and Lebanon. The result is the much-lauded book American Apostles: When Evangelicals Entered the World of Islam.

An expert in American history from European settlement to the Civil War, Heyrman says she had a pretty good idea where to begin—“by looking at religious folks.” She found them in New England, in the detailed diaries written in the 1820s by the first American missionaries to the Middle East. Levi Parsons and Pliny Fisk journeyed to the Levant, an arc of land along the eastern Mediterranean, to found the Palestine mission, followed a few years later by Jonas King.

“They were country boys who had wide-eyed, idealistic expectations to convert this stronghold of Islam to true Christianity,” Heyrman says.

Although their crusade failed, Heyrman says the weekly reports they mailed home, altered where necessary by pious editors, were “treated as gospel” and became “the fodder for the dreams and fantasies” of Americans in this age before photography. Readers were enthralled by such wonders as Mount Lebanon and the famous cedars at its base—the largest 40 feet around—and how Arab sheikhs greeted male friends by grasping hands, then “put their foreheads together and smacked their lips but without bringing their faces into contact.”

These young missionaries didn’t preach to large crowds or set up schools. Their chief role was to travel and gather information. But acquiring all of this knowledge had unintended consequences.

“Today, people have the idea that evangelicals are far more likely to have a negative view of Islam,” Heyrman says. “While that’s certainly true at the outset for these early missionaries, some ended up being more accepting of Islam.”

Just as these first missionaries expanded their views, Heyrman hopes the book will convey the importance of trying to understand other religious traditions.

In a private journal, Fisk chronicles his encounters with individual Muslims, lessons in Arabic and instruction in the Qur’an. He keeps noticing where Christianity and Islam are alike and develops an appreciation of Islam as a faith.

“He is fascinating in his ordinariness,” Heyrman says of Fisk. “Here’s this Yankee from a poor farming family, previously committed to the evangelical cause. Watching him change was intriguing to me because it was so unexpected.”

King, however, is the militant crusader who finds “inspiration in his embattled encounters with Muslims to endow his kind of Christianity with an indisputable purchase on masculinity.”

“Fisk is a real seeker of other faiths, and you see the possibility of his being an honest broker,” she says. “Conversely, King wants to use the whole Middle East to suit his ambitions—plenty of people are like that today. We need to be more like Fisk and less like King who sees the Middle East as an idealogical opportunity.”

Earlier this year, the Society of American Historians awarded American Apostles the 2016 Francis Parkman Prize. It is presented annually to a nonfiction book that is distinguished by its literary merit and makes an important contribution to the history of the United States.