“This looks like the last straw,” a seething President Harry Truman scrawled in his diary on April 6, 1951. Once again the commander of U.S. forces in the Korean War, General Douglas MacArthur, had gone public with his differences with the commander in chief over the conduct of the war—this time in a letter to House Republican Leader Joseph Martin.

Truman thought it nothing less than “rank insubordination,” and five days later he delivered the shocking news to the American people that he had relieved MacArthur of his command and replaced him with General Matthew Ridgway. “With deep regret I have concluded that General of the Army Douglas MacArthur is unable to give his wholehearted support to the policies of the United States Government and of the United Nations in matters pertaining to his official duties,” the president said.

The tension that had been mounting for months between the modest president and the egotistical general went beyond mere personality differences. Still upset that MacArthur had mistakenly assured him during a face-to-face meeting on Wake Island that the communist government of China would not intervene on behalf of North Korea, Truman favored a “limited war.” MacArthur, however, publicly advocated the more expansive use of American military power, including the bombing of China, employment of Nationalist Chinese forces from Formosa (Taiwan) and the possible use of nuclear weapons. Fearing that such an approach risked a massively expanded war in Asia and even the start of World War III—with the Soviet Union coming to the aid of China—Truman clashed repeatedly with MacArthur before finally dismissing him.

Truman’s decision had far-reaching implications beyond just the conduct of the Korean War, according to H.W. Brands, author of the The General vs. the President: MacArthur and Truman at the Brink of Nuclear War. “I think the enduring legacy is that Truman took a great political risk, and he did it immediately to prevent World War III, but also to prove the principle that civilian elected officials are above military officials, however grand and decorated they may be,” Brands tells HISTORY.com. “Generals ever since have taken that lesson. With Lyndon Johnson, the generals in Vietnam knew not to take their differences outside of the administration or popular opinion would probably be against them.”

Truman’s decision not only ended MacArthur’s military career, it ended the president’s political career as well, setting the stage for the subsequent presidency of Dwight Eisenhower. In the first 24 hours after the president’s announcement, the White House received more than 5,000 telegrams—three-quarters of them backing the popular MacArthur, who had been named the greatest living American in a 1946 poll. “In the wake of the firing, Truman’s popular approval rating set a record not matched before or ever since—22 percent—lower even than Nixon’s at the depth of the Watergate scandal,” Brands says. After what the historian calls “political suicide,” Truman did not even pursue his party’s nomination in 1952.

MacArthur, however, harbored ambitions of succeeding Truman as commander-in-chief after returning home to a hero’s welcome that included an address to a joint session of Congress and a ticker-tape parade through New York City. “There was this popular surge of support for MacArthur when he came home, but it turned out it was for what MacArthur had done in the past rather than what he might do in the future. He was the last of the generals to come home and get his victory parade,” Brands says. “MacArthur read it as possible support for a MacArthur candidacy for president. It turned out that wasn’t it.”

MacArthur’s support among right-wing Republicans began to sag after a Senate committee heard secret testimony from his superiors, including Generals George Marshall and Omar Bradley, that disputed the viability of MacArthur’s plan for a total war and revealed the United States lacked the military capability at the time to win another world war. “It demonstrated that MacArthur was just talking hot air, and very silently the air started to leak out of the MacArthur balloon,” Brands says.

When MacArthur’s keynote speech at the 1952 Republican National Convention fell flat, delegates abandoned the general. “They turned to another general—one with a more common touch, Eisenhower,” Brands says. “MacArthur’s political balloon sank to earth and was never seen again.”

The two competing visions of Truman and MacArthur as to how to respond to the threat of communism and wage war in the nuclear age reverberated for decades after Eisenhower brought the Korean War to a conclusion. “Truman thought the Cold War could be won without an all-out war with the Soviet Union, but MacArthur did not believe that was possible,” Brands says. “MacArthur essentially believed that World War III had begun and the U.S. had to wage it. He believed there was no substitute for victory.

“MacArthur thought that if we go to war, we go to war. Any commander in battle wants to protect those forces, and to send men into battle knowing he can’t use all potential resources is exceedingly frustrating. That’s going to get any general upset,” Brands says. “World War II, however, was the last war that Americans have been able to fight all out. The reason is that the dangers of escalation outweigh the benefits of victory.”

Total war was no longer possible in a world in which other countries, including the Soviet Union, had the atomic bomb as well as the United States. Brands says Truman’s notion of a limited war may have been a reality of the nuclear age, but it wasn’t as satisfying as the previous policy of unconditional victory. “World War II created the model war in American minds—a war where we take the gloves off, we win and we come home. The Cold War wasn’t like that. It was very unsatisfying for Americans. It was a world that took some adjusting to.”

Brands says the “end of the Cold War on the terms that Truman had pioneered,” including “firm, patient resolve,” vindicated the president’s approach in his showdown with the general. As he writes at the close of his book, “The courage of Truman’s decision had never been in question; six decades later, its wisdom was apparent as well.”