The United States came fairly close to using nuclear weapons in the Korean War. That risk is always present when a nuclear-armed power is losing a conventional war.  The main thing that restrained President Truman was the successful amphibious landing at Inchon, which turned the war in America’s favor.

[In August 1950], again on the president’s orders, the Strategic Air Command sent 10 atomic-capable B-29s, also carrying assembled bombs without their plutonium cores, to Guam. They were soon augmented by 10 more bombers. For the first time since 1945, atomic bombs, complete but for the nuclear cores, were transferred to military custody. All that was needed was someone to light a match.

Then everything changed.

On September 15, U.N. forces, spearheaded by U.S. Marines, carried out an amphibious landing at Inchon, about 20 miles west of Seoul. MacArthur had long argued for this counter-strike, but the tactic had been vetoed as too risky.

The Inchon landing turned out to be a brilliant flanking attack. U.N. forces quickly retook Seoul and severed the North Koreans’ supply lines. Walton Walker’s Eighth Army broke out of the Pusan Perimeter and formed up with other allied units. By early October, American forces had pushed across the 38th parallel and taken the North Korean capital, Pyongyang. Before October was out, U.N. forces had advanced to the Yalu River. The war, most observers believed, would be won by Christmas.

Of course, the war then turned back in the communists’ favor when China invaded from the north. They hadn’t been dissuaded by the nuclear threat in Guam, but Truman hoped making the threat more explicit might help.

With the Chinese intervention, the United States confronted a hard truth: Threatening a nuclear attack would not be enough to win the war. It was as if the Chinese hadn’t noticed—or, worse, weren’t impressed by—the atomic-capable B-29s waiting at Guam.

President Truman raised the ante. At a November press conference, he told reporters he would take whatever steps were necessary to win in Korea, including the use of nuclear weapons. Those weapons, he added, would be controlled by military commanders in the field.

He also made sure using nukes was a real option.

In April of the next year, Truman put the finishing touches on Korea’s nuclear war. He allowed nine nuclear bombs with fissile cores to be transferred into Air Force custody and transported to Okinawa. Truman also authorized another deployment of atomic-capable B-29s to Okinawa. Strategic Air Command set up a command-and-control team in Tokyo.

This spate of atomic diplomacy coincided with the end of the role played by Douglas MacArthur. After MacArthur had publicly and repeatedly differed with the president over military strategy in Korea, Truman replaced him with General Matthew Ridgway, who was given “qualified authority” to use the bombs if he felt he had to.

A variety of factors prevented the use of nuclear weapons. For one thing, we didn’t have that many of them and there were doubts about their effectiveness against waves of infantry in a mountainous region.  There was also world opinion to consider, and the defense of South Korea was a United Nations mission.

When America discovered it could not win the Vietnam War or end it on acceptable terms, the idea of using nuclear weapons was considered again. But by that time, there were several nuclear powers and the weapons were far more powerful. It was understood that a nuclear confrontation could end life on earth, and the taboo against limited use held. America accepted defeat without using nukes, and did so again in Iraq and Afghanistan.

The Soviet Union also accepted defeat in Afghanistan without using nuclear weapons, but it’s quite possible that losing in Ukraine just isn’t an option for Vladimir Putin. He won’t lose overnight, of course. But he may discover that he can’t end the war on acceptable terms.

It seems impossible that he could stay in power without achieving his objectives in Ukraine. In fact, his biggest threat is the Russian people who may turn against him. Discontent within his military can take two forms, one of which is insisting on using nukes and the other is removing Putin in a coup.

The problem here is obvious. The worse things go for Russia, the more likely it is they use nukes. Yet, if Putin easily wins and crushes all resistance in Ukraine, he will set his sights next on NATO members like the Baltic states.

Now, to be sure, Putin wouldn’t drop a hydrogen bomb on Ukraine because Russia would get the fallout.  But he might use smaller tactical nuclear weapons to subdue urban populations.

The more I think about these things, the angrier I get with Putin for starting this fight. He’s an absolute monster.