“We have some great plans should, as we say, ‘the balloon go up’ in Korea,” Gallego, a former Marine, told me. “I know what happens with plans when the first bullet goes flying. … What I fear is that someone like Donald Trump will look at these great plans, look at our great military, which it is, look at their great capability, which we have, and not understand that these are not superhumans—that if we do something wrong, we will potentially kill hundreds of thousands of people, including some of our own troops, and potentially disrupt a good portion of the world’s economy for years to come.” And that’s considering only the early stages of battle and assuming the conflict doesn’t go nuclear.

“You’re basing policy and military action on hopes instead of on reality and sound reasoning,” Gallego said. “Does this sound familiar? For me it does, as somebody who ended up serving on the front lines of the Iraq War, where I was supposed to be greeted as a liberator. Instead I basically got shot at every day.”

Robert Neller, the commandant of the U.S. Marine Corps, acknowledged the limitations of military plans during an appearance at the Center for Strategic and International Studies on Thursday. “If [a U.S. conflict with North Korea] were to go down, I’m not now so sure it’s going to go down the way we planned. It never does,” he said. Neller stressed that he hopes such a fight never breaks out. Nevertheless, “we want to be ready, and we want to have a capability that allows our diplomats to come up with a diplomatic solution.”

Neller said he and other heads of the armed services have gotten “familiar with the geography … [and] the plans” and done “some logistical preparation that’s just prudent.” He added that U.S. Forces Korea and U.S. Pacific Command are busy training, conducting exercises, and exploring “force deployment options” to convey to the “other side” that “you really don’t want to do this.” Meanwhile, the other side is making its own preparations. Alexander Vorontsov, a Russian Korea scholar, recently wrote that North Korean Foreign Ministry officials he visited in Pyongyang in November told him they did “not want war” but would “not hide from it either.” They “feared that the U.S. was already trying to shape the battlefield for a military operation against the North.” And, Vorontsov continued, the North Korean government “is not bluffing when it says that ‘only one question remains: When will war break out?’ … [O]ur counterparts emphasized that ‘our soldiers have long been sleeping without removing their boots.’”

In such circumstances, Gallego worries that “we [could] trip ourselves into a war” no one wants—if, “for example, the North assumes one of our moves is a strike and they decide to do a preemptive strike.” Neller might respond that one of the points of U.S. military preparations is to prevent war by deterring the adversary. And perhaps war will indeed be averted. Then again, perhaps not. As the World War I historian Margaret MacMillan told me not long ago, “Once you get into a countdown situation, once people begin to think of war as likely, then it becomes that much more likely”—whether as a result of deliberate decisions, tragic miscalculation, or mere mistake.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.