Historian Andrew Preston first became interested in the overlap between religion and America's foreign policy decisions while teaching an undergraduate class on American foreign policy in the days leading up to the 2003 invasion of Iraq.
"My students took it for granted that [Osama] bin Laden would use extremist rhetoric, [but] they were more surprised by [President George W.] Bush's use of religious imagery and religious rhetoric to explain American foreign policy," Preston tells Fresh Air's Terry Gross. "And they asked me if this was unusual in American history, if presidents turned to religion very often. ... I told them that I'd find out some more. I said that in general, I thought that religion didn't play much of a role in U.S. foreign policy."
But Preston says he wasn't convinced of his own answer. He decided to research the topic further, only to find that historians had largely overlooked the relationship between religion and foreign policy throughout American history.
"And once I started looking at the documents, once I started looking for religion, it was everywhere," he says. "And I thought, 'This would be something I'd like to work on.' "
The result is his book Sword of the Spirit, Shield of Faith, which traces how religious language has been invoked to support U.S. foreign policy decisions throughout the country's history and up to the present day.
Preston explains, among other things, how Abraham Lincoln's use of religious rhetoric during the Civil War helped influence later humanitarian missions, and how religious liberty was a major factor for Franklin Delano Roosevelt when thinking about the U.S. role in World War II.
Even before the country was founded, Preston says, early settlers used their religious doctrines to frame their thinking. The earliest settlers to the New World came looking for a haven from religious prosecution, but also wanted to protect their faith from opponents throughout Europe.
"At various points it looked like it might not survive," he says. "So at various points, the [early settlers] wanted to bring the Protestant faith to the New World to keep it safe and let it grow."
The Puritans ended up identifying the protection of their Protestant faith with their own physical security, he says.
"They believed that not only did they have to protect that idea to protect themselves, but they believed that they had to spread it," he says. "And by spreading that idea, they would ensure its survival, ensure its prosperity, and then they would ensure their own survival. And this kind of exceptionalism has been fairly constant and continuous in American history."
Preston points to the charter of the Massachusetts Bay Colony — the group that would found the state of Massachusetts, which clearly states that its primary goal was to "incite the natives to the knowledge and obedience to the only true God and savior of mankind."
"They had some strong ideas about their own faith and their own virtue and the virtue of their own faith," he says. "These people who founded Massachusetts, they were seeking religious liberty and they were complaining about the persecutions they suffered in England. And of course, the first thing they do when they get to Massachusetts is persecute others and persecute their religion."
Since its founding, Preston says, America has seen itself as "God's chosen nation."
"It is a very powerful strand," he says. "Part of it comes from the Protestant faith that some of the first colonists brought over with them: a Calvinistic belief in providence that God had a plan for people, that God had chosen people and that Americans were one of those peoples — they were God's instrument on Earth to do good and to rid the world of evil."
Preston says he thinks this belief still exists in the country today.
"I think a lot of Americans believe that, and I think it provides a very strong motivation for people calling for America to act the way it does in the world," he says. "You can see it in the rhetoric around quite a few wars. You could see it in the rhetoric in George W. Bush's language in justifying the war in Iraq. Whether that decision was right or wrong ... I don't take a stand on that, but that sort of idea — that America is chosen ... was all over Bush's rhetoric. But Bush was certainly not an aberration in American history. He was actually quite typical."
On religion providing some of the core ideas for the founders of the United States
"Even people like Thomas Jefferson or George Washington, who weren't very religious ... saw religion as the source of conscious morality, and therefore you had to protect religion almost at all costs. And Thomas Jefferson ... who certainly didn't have any faith in the divinity of Christ, even he believed that you had to protect individual conscience and therefore you had to protect religion. But in order to protect that, and to prevent ecclesiastical tyranny, you had to separate church and state — and that's where these early ideas emerged."
On the separation of church and state
"The First Amendment has the free exercise clause and the establishment clause, and that's pretty much it. And how that was interpreted for the first 150 years was that religion had a role in public life, religion had a role in politics. It just meant that the government couldn't regulate religion; it couldn't set up a national church, and it couldn't interfere with the way people worshipped. Essentially what it did was make Protestantism the unofficial religion. That only changed after World War II, when our nation became more religiously pluralistic and other groups like Catholics and Jews started challenging the Protestant domination. The Supreme Court decided to make things more simple for a modern era by hardening what Jefferson called the 'wall of separation between church and state.' The best thing to do was to try and remove religion from public life as best as people could."
On FDR and foreign policy
"FDR by 1937 wanted the United States to play a more active role in world affairs and a much more active role in resisting Nazis – maybe not to go to war, but certainly to take a more active role in resisting Nazism. And he constantly evoked both 'the sword of the spirit' and the 'shield of faith' in overtly religious language – speaking of religion by name and quoting from the Bible, and especially pointing to the threat the Nazis posed to all religions. And he used the 'sword of the spirit' to call for a robust American foreign policy. But he also used the shield of faith to couch it in terms that were very much about implementing world peace and spreading democracy."
On American exceptionalism
"To most people it means that America is exceptional in that it's not only different, but it's better. And often it's better because of those differences. And America is a unique force of good in the world, a unique force for virtue. And exceptionalism usually applies to people who believe that America should spread this virtue or should share it in the rest of the rest of the world, and often that results in conflict and/or war."
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