In On Desperate Ground: The Marines at the Reservoir, the Korean War’s Greatest Battle (Doubleday, Oct.), historian Sides revisits the epic clash between U.S. Marines and the Chinese soldiers who vastly outnumbered them.

What interested you in this battle?

Mostly I was drawn to these stories because Korean War veterans are part of the generation we’re saying goodbye to now. My stepfather, who recently passed away, was a Korean War veteran, and my father in-law had orders to go there, so there’s no way for me to escape the emotional significance. And at its essence, this is a military survival story. The story of Lee-Bae Suk [a young Korean man who served as a Marine interpreter and whose family was divided by the fighting] and the gratitude he feels toward Americans was so moving, I decided to give him a lot of space. In a way, he is a stand-in [in the book] for hundreds of thousands of Koreans, on both sides of the 38th Parallel.

You write that U.S. soldiers saw Korea as a sort of pointless place to die. How did the veterans you talked to think about it now?

There was a generational reticence about discussing it. But with some of them, when they did talk, it really opened the floodgates. This was a surreal experience for them—fighting at night, the waves and waves of Chinese soldiers, the bugles and cymbals and the screaming. They’re still processing it. Some of them say they still wake up cold, that they can’t get the cold out of their bones. A lot of them have returned to South Korea, partly because the South Korean government formally invites veterans to come. They said seeing Seoul, not the battered and destroyed city they fought in, but this modern metropolis that’s the capital of the 10th largest economy in the world, made them feel like it was all worth it. You only have to look across the DMZ to see what South Koreans’ existence could be like.

What should the modern reader take away from this account?

This battle should never have occurred. It happened because the leaders of China, North Korea, and the United States were not talking with each other. If the intelligence had been better and there had been more careful diplomacy, this tragic collision could have been avoided altogether. This was also an example of asymmetrical warfare. Mao had a peasant army wearing tennis shoes, and many of them didn’t even have weapons. And we were this modern vehicular army. We were, in a sense, slaves to our technology; we were tied to the road. The Chinese always knew where to find us. And there’s still that kind of asymmetrical warfare going on today. That’s certainly true in Afghanistan. People are always surprised when seemingly primitive forces inflict so much damage on a modern army like ours. This was a perfect example of it.