What Actually Happened

In September 1950, the National Security Council issued Report 81/1, entitled “United States Courses of Action with Respect to Korea,” which outlined the council’s official recommendation on the question of whether to invade North Korea. It concluded that “the United Nations forces have a legal basis for conducting operations north of the 38th parallel” and that 

the UN Commander should be authorized to conduct military operations, including amphibious and airborne landings or ground operations in pursuance of a roll-back, north of the 38th parallel for the purpose of destroying the North Korean forces, provided that at the time of such operations there has been no entry into North Korea by major Soviet or Chinese Communist forces, no announcement of intended entry, nor a threat to counter our operations militarily in North Korea. 

On September 15, UN forces landed at Inchon, backed by naval and air bombardment. The landing was an extraordinary success. It stunned the North Korean forces and forced them into withdrawal. By the end of September, South Korean and UN troops had recaptured Seoul and officially restored the South Korean government under Syngman Rhee.  On October 1, General Douglas MacArthur officially demanded North Korea’s surrender. Receiving no reply, he authorized South Korean forces to advance across the border. UN forces followed closely behind once they received authorization. This authorization came on October 7, with a UN General Assembly resolution calling on UN forces to take “all appropriate steps . . . to ensure conditions of stability throughout Korea.” 

Within the first few weeks of their attack, UN forces moved rapidly northward. Facing little resistance from the retreating North Korean soldiers, UN and South Korean forces advanced swiftly and captured Pyongyang on October 19. But things did not continue as smoothly. On October 25, Chinese forces began operations against South Korean forces. It would be more than a month before the United States acknowledged that China was mounting a full-scale intervention in Korea. By then, UN forces were being pushed south, their gains since crossing the thirty-eighth parallel quickly reversed. Seoul fell for the second time in January 1951. Three months later, Truman fired MacArthur. 

After a series of bloody attacks and counterattacks, UN and Chinese forces met at the thirty-eighth parallel in a stalemate in the spring of 1951. For the next two years of fighting, they only made moderate gains and losses of ground around the parallel. On July 27, 1953, China, North Korea, and the UN Command signed an armistice, bringing an end to the fighting. Though the agreement was meant to establish a ceasefire “until a final peaceful settlement is achieved,” no settlement was ever agreed on. To this day, the two Koreas are still officially at war, and the thirty-eighth parallel has become the most heavily militarized border in the world. 

The effects of the war were acutely felt on the peninsula, where more than two million were killed—as many as 70 percent of them civilians. The United States dropped more explosives on North Korea during the three-year conflict than in the entire Pacific theater during World War II. As a result of bombing,  an estimated 85 percent of buildings in the country were destroyed. 

What did the decision mean? 

Though largely forgotten by—or unknown to— many in the West, the Korean War’s effects have shaped geopolitics and reverberated through history. The war cemented alliances and rivalries that endure today, ushered in policies that would characterize many years of the Cold War, and finalized the thirty-eighth parallel as an enduring dividing line on the Korean Peninsula.

Solidification of Alliances and Rivalries 

The Soviet Union and China continued to economically and politically support North Korea throughout the Cold War, as the United States did South Korea. Two months after the armistice was signed in 1953, the latter pair cemented their alliance with the Mutual Defense Treaty Between the United States and the Republic of Korea, establishing a powerful military alliance underwritten by American nuclear weapons. 

Despite the collapse of the Soviet Union in 1991, these relationships are still largely in place today. Today, South Korea hosts over twenty thousand American troops, and North Korea maintains relatively close, though sometimes fraught, relationships with Russia and China. 

Cold War Policies 

The Korean conflict heralded many of the hallmarks of U.S. foreign policy during the Cold War. One of those was the concept of limited war—a war in which limited resources, forces, and tactics are used in service of goals significantly short of total destruction of the enemy. Because the United States and the Soviet Union were both wary of triggering a general—­and quite possibly nuclear—war, they became involved in limited proxy conflicts during the Cold War. The Korean War would be followed by similar conflicts in Vietnam and Afghanistan. Hand in hand with this policy was the doctrine of containment, which advocated for “containing” the spread of communism within national borders (and which had served as Truman’s primary rationale for entering the Korean War). In many ways, the Korean War became a blueprint for how the Cold War would be fought.

An Enduring Division 

Perhaps the most significant legacy of the Korean War is the enduring division of the Korean Peninsula. Since its establishment as an arbitrary administrative boundary in 1945, the thirty-eighth parallel has remained the dividing line between North and South Korea. 

Since the armistice was declared, relations between North and South Korea have ranged from conciliatory to combative. Particularly in the last few decades, the peninsula has seen a few near brushes with war. In 2006, after years of development, North Korea ratcheted up the tension by testing its first nuclear weapon. (South Korea remains under the U.S. nuclear umbrella, meaning that the United States has pledged to defend South Korea from any nuclear attack). According to scholar Bruce Cumings, North Korea’s generals “are still fighting the war. For them it has never ended.” 

Was it a good idea? 

Many accounts of the Korean War frame the decision to cross the thirty-eighth parallel as a mistake. Bruce Riedel of the Brookings Institution calls it “by far the worst military debacle the U.S. armed forces suffered in the entire twentieth century” and a “catastrophic intelligence failure . . . that cost the lives of thousands of Americans.” Similarly, historian Warren Cohen writes that the Truman administration, “in its moment of triumph . . . succumbed to one of the most treacherous temptations confronting any victor, the temptation to expand war aims.” 

Journalist and U.S.-China relations scholar John Pomfret argues that the United States’ biggest mistake was in underestimating the potential for Chinese involvement; he reports that General Matthew Ridgeway, who had led operations in Europe during World War II, noted that General MacArthur “‘simply closed his ears’ to the growing presence of Chinese troops in Korea.” Similarly, scholar Robert Farley argues that “the initial Chinese victories in late fall of 1950 resulted from a colossal intelligence failure on the part of the United States. These failures ran the gamut from political, to strategic, to operational, to tactical. . . . The United States also misunderstood the complex relationship between Moscow, Beijing, and Pyongyang, treating the group as unitary actor without appreciating the serious political differences between the countries.”

Other scholars, however, are more sympathetic to the decision’s historical context. Scott A. Snyder of the Council on Foreign Relations argues that “it would have been difficult to imagine that any commander . . . would have made the decision to simply halt in the face of what looked like an open field up to the China and North Korea border.” Historian William Stueck also defends the decision, arguing that by the time the threat of Chinese intervention became credible, the decision to advance had already gained too much momentum: “to delay action would have disappointed expectations in the United States in the midst of a congressional election campaign, would have compromised a clear military advantage, and would have constituted an apparent loss of nerve in the face of Communist pressure tactics."

In sum, scholars debate whether the decision to cross the thirty-eighth parallel represents a failure to assess intelligence and understand Chinese and Soviet motivations or a calculated decision to consolidate victory and demonstrate commitment to broader foreign policy goals. But the legacy of the war remains certain: the lasting division between North and South Korea has remained a critical foreign policy challenge to this day.