When it comes to longevity, the Catholic church has Protestantism beat by roughly 1,500 years. But Protestants are the clear winner in terms of producing epic drama over the past five centuries.

Their story "can be told as one long argument," writes Alec Ryrie, a British historian of Christianity in his perceptive and opinionated new book Protestants: The Faith That Made the Modern World.

But Ryrie, a Protestant himself and lay preacher within the Church of England, believes this mammoth collection of faiths-within-a-faith is much more than just a never-ending fight within a theological thunderdome. "From the beginning," he writes, "a love affair with God has been at its heart."

Here are five surprising facts from "Protestants" about the faith's five-century journey.

1. Martin Luther had a crisis of ... pragmatism

When you're fighting the immense power of the Catholic Church, as Martin Luther was in the 1500s, you need powerful allies. That's where princes came in.

But the preachers needed the princes more than the reverse, Ryrie writes, "and both sides knew it." This went "badly wrong" when a lusty German prince came to Luther with an indecent proposal: Let me have a second wife or else I'll go see what the Pope has to say about it.

Luther gave in but unsuccessfully tried to keep the bigamy secret. The world learned about an ends-over-means decision that "permanently stained Luther's reputation." Pragmatism had won out over principle in a man devoted – at the risk of his own life – to the latter.

2. Freedom of conscience had its limits

In their first century of existence, Protestants began developing the idea of freedom of conscience. "This tradition is inspiring," Ryrie writes, "but had its limits."

That's because philosophers and even Luther himself distinguished between freedom from coercion (being forced to believe something) and freedom of belief (being able to believe whatever you want).

So beliefs considered to be dangerous (like Catholicism) or blasphemous (like atheism) could still be outlawed.

Still, the very idea of toleration was a remarkable development. Citizens in one nation – the Netherlands – went so far as to not kill people over their beliefs, another step forward toward modernity.

3. Protestantism faced an early close call

"A dispassionate observer in the 1660s might well have concluded that Protestantism was doomed," Ryrie writes.

The faith faced threats from Catholics, skepticism, and division, not to mention mysticism and an early form of atheism. Its reaction was to gird for battle "on the principle that those who were given an inch would take a mile."

Protestants could have manned the ramparts until there was nothing left to defend. The Enlightenment, Ryrie contends, inspired them to stand "on the side of the new."

At the same time, he writes that Protestants found a new way forward through the rise of evangelicalism, which emphasized a personal, deeply intimate connection with God – firing up that "love affair."

4. The faith often left many slaves behind

African-Americans and Protestantism have been deeply intertwined since the days of slavery. But this was not preordained. Slaveholders were often "openly hostile" to allowing their slaves to embrace Christianity, Ryrie writes.

Among the fears: Slaves would refuse to work on Sunday, they'd undergo Christian marriages and form unbreakable unions, they'd feel inspired to seek freedom. And, some slaveholders argued, slaves weren't human anyway, even though "such views were theologically indefensible."

At times, missionaries paid with their lives for daring to try to convert slaves. They tried to fight back by saying Christian slaves would be better slaves.

But Protestants – including Methodists, Baptists and Presbyterians in the US – began to believe slavery was a deep wrong. Some even insisted that Jesus and the apostles hadn't opposed slavery in the biblical era because the time wasn't yet right for such a message.

5. In South Korea, a faith all its own

South Korea is home to millions of Protestants, the world's largest church (with about 750,000 members), and the second-largest contingent of missionaries (20,000) after the US. Its brand of faith is unique, Ryrie writes.

According to him, Protestants in South Korea, more than anywhere else in the world, focus on the book of Revelation, the so-called Rapture, and the end of the world.

Ryrie suggest that the roots of this lie in Korea's past under the grip of Japan. Faith, he believes, gave Koreans something they could control – repentance – and a way forward beyond the difficulties of this world.

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Even now, there's a sense, he writes, "of Korea as an apocalyptic nation, claiming a late but crucial place in the world's salvation history."

And so the "very long argument" of Protestantism continues, as vibrant, diverse and confounding as ever.