Never Truly Forgotten: The Lethal Legacy of the Korean War


Seventy years after the Korean War’s outbreak, the peninsula is teetering on the precipice of yet another North-South crisis. With growing bombast, North Korea has overturned several years of de-escalatory diplomacy, ratcheting up its threatening rhetoric and sending an unmistakably menacing signal with the explosion of the Inter-Korean Liaison Office. Despite the Trump administration’s attempts at negotiation, Washington’s strategy of “maximum pressure” is manifestly discredited — North Korea has a substantial and growing nuclear and missile program, and has rejected denuclearization as “nonsensical.”

The specter of renewed conflict is a dangerous but fitting marker for the Korean War’s 70th anniversary. Though often disregarded as a “forgotten war” — overshadowed by the global conflagration that preceded it and the nation-rending counter-insurgency campaign in Vietnam that followed it — the 1950–53 conflict on the Korean Peninsula remade Cold War history, with aftershocks that reverberate through today’s crisis. The war entrenched the division between North and South, along with China’s patronage of the former and America’s alliance with the latter. By elevating Washington’s estimate of the communist threats emanating from Asia and especially Beijing, the Korean War contributed to a vast expansion of the United States’ overseas defense commitments — not only in South Korea, but in Japan, Australia, New Zealand, Taiwan, and Indochina as well. To uphold these new partnerships, the United States pivoted from a posture of post-World War II demobilization toward investment in forward defense as the central pillar of its Cold War strategy. These durable effects demonstrate how crises can alter history’s course and underscore the vital importance of effective American policy at a moment when so much of the future of international affairs, in Asia and globally, remains up for grabs.

The Forgotten War

The Korean War began when North Korean forces crossed the 38th parallel — a division imposed at the end of World War II — and invaded South Korea. The offensive caught the United States unaware and unprepared. After a postwar period of occupation, American combat forces withdrew from Korea in 1949, leaving behind a 492-man military advisory mission, and Washington sought to buttress the South Korean government through economic and military aid. It calculated that Korea held limited strategic value in a prospective global hot war between the United States and the Soviet Union — a sentiment that Secretary of State Dean Acheson broadcast in January 1950 when he implied the Korean Peninsula was outside of the American defensive perimeter. Though hardly intended as an invitation, Washington’s perceived disinterest in protecting South Korea militarily contributed to Soviet Premier Josef Stalin’s decision to finally greenlight North Korean leader Kim Il Sung’s plan to reunify Korea via force.



With the United States caught off guard, North Korea initially made a herculean advance down the peninsula. The North’s assault troops outnumbered those of the South by approximately 24,000, and about half of North Korean forces had fresh combat experience from participation in the Chinese civil war. North Korea’s advantages in tanks, artillery, and aircraft — augmented by assistance from Soviet military planners — proved initially decisive. By June 28, Seoul had fallen.

Washington quickly deemed the invasion an unacceptable act of aggression and moved to intervene under United Nations auspices. Over the ensuing weeks, with the support of the U.N. Security Council, the United States massed troops on the Korean Peninsula to mount a defense of South Korea. Yet even after the introduction of American troops and airpower as part of a U.N. coalition, North Korean troops  continued to advance — all the way to Korea’s southeastern tip. It was not until the Incheon landing in September 1950 that the war’s momentum turned in the coalition’s favor. Flush with success, Gen. Douglas MacArthur, the commander of the U.N. troops, launched an “end-the-war” offensive, advancing close to the Chinese border. Then, in late October 1950, the trajectory of the war changed once again when 260,000 Chinese troops crossed the Yalu River and forced U.S. troops into the longest retreat in American military history. Over the six months that followed, the U.N. coalition supported South Korea in a bloody war of movement against North Korean and Chinese forces receiving nominally covert aid from the Soviet Union (which was not well concealed but nevertheless remained clandestine as both sides attempted to manage escalation pressures by avoiding publicity).

Despite its emergence as the blazing front line of an increasingly frosty Cold War, the Korean War remained limited. Whereas American strategy had assumed that any clash with communist forces would metastasize into a total war, conflict in Korea inaugurated a new genre of limited conflict fought under the nuclear shadow. Even as military victory remained elusive, Washington decided against escalating the war by using atomic weapons or attacking Chinese territory with aircraft. Indeed, by June 1951 — one year after the North’s invasion — a stalemate began to coalesce along with a first round of negotiations. Over the two years that followed, the parties intermittently talked and fought — the battle lines did not change significantly, but prolonged gridlock regarding the disposition of prisoners of war hindered a settlement until an armistice was finally signed on July 27, 1953.

Containment Before Korea

The Korean War reshaped American strategy and, by extension, the Cold War’s subsequent course. Before its outbreak, the United States subscribed to a minimalist strategy of containment. In 1948, the National Security Council (NSC) issued NSC 20/4 — the most comprehensive statement of American strategy prior to the Korean War — which said the “will and ability of the leaders of the USSR to pursue policies which threaten the security of the United States constitute the greatest single danger to the U.S. within the foreseeable future.” Yet World War III did not seem imminent, and cutting national security spending was a paramount political priority, as policymakers sought to control inflation and maintain a balanced federal budget. Between 1945 and 1947, the U.S. military shrank from 12 million to 1.5 million troops and, in parallel, the defense budget contracted by more than 80 percent.

Underwriting this strategic wager was the security derived from American atomic superiority over the Soviet Union. Although Moscow had tested its first nuclear device in August 1949, the United States had an important head start. Moreover, as of January 1950, the United States was actively pursuing a thermonuclear weapon. As Gen. Matthew Ridgway, who led the U.N. coalition in Korea from April 1951 to May 1952, reflected:

The atomic bomb created for us a kind of psychological Maginot line that helped us rationalize our national urge to get the boys home, the armies demobilized, the swords sheathed, and the soldiers, sailors, and airmen out of uniform.

Instead, the Truman administration expected measures short of war — propaganda, diplomatic pressure, political subversion, and economic and military aid to friendly governments —to be the predominant modes of Cold War competition.

While preventing Soviet domination of Eurasia was the overriding priority, Europe enjoyed clear primacy over Asia in the Truman administration’s pre-Korea strategic planning. As Acheson explained:

If anything happens in Western Europe the whole business goes to pieces, and therefore our principal effort must be on building up the defenses, building up the economic strength of Western Europe, and so far as Asia is concerned, treating that as a holding operation.

Moreover, with the newly victorious Chinese Community Party’s focus seemingly focused inward, U.S. strategists proceeded on the assumption that the risk of war in Asia was low. American political support and aid was therefore judged sufficient to prevent communist subversion or aggression. This logic guided Washington’s decision in 1949 to withdraw its troops from Korea.

Some scholars contend that prior to the North Korean invasion of South Korea, the United States was already moving away from this modest strategy. According to this view, a series of geopolitical setbacks — most notably the Soviet nuclear test and the communist victory in China’s civil war — catalyzed a rethink of American national security policy. This process of strategic reevaluation resulted in the NSC 68 document, which is often portrayed as a critical point of departure — the moment at which the United States turned away from a minimal version of containment, as envisioned by the doctrine’s architect George Kennan, and toward a maximalist posture that set the United States on a course of wanton military spending propelled by expansive threat assessments. Without question, NSC 68 presented a far direr assessment of Soviet intentions and was consequently more bullish on defense expenditures than preceding strategy statements. But it was also intentionally vague about spending levels and lacked presidential endorsement until after the Korean War broke out. If the Korean War had never happened, it is unlikely that the implementation of NSC 68 would have produced changes of a remotely similar magnitude to the ones that began with the war’s outbreak in June 1950.

Cold War Crucible

The Korean War demonstrated Washington’s prevailing strategy to be untenable. From the perspective of leaders in Washington, in permitting the invasion, Moscow seemed willing to pursue territorial expansion via its proxies, even at the risk of general war — heralding far more aggressive intentions than American policymakers previously assumed. Whereas China had appeared to be focused inward on reconstruction after its recently concluded civil war, its intervention in Korea exhibited the surprising effectiveness of its military forces and announced Beijing’s willingness to accept high costs — more than a million casualties and the risk that the war would escalate across the Yalu River, possibly with American nuclear weapons — in support of its North Korean neighbor. Even North Korea proved more capable militarily than U.S. intelligence assessments had previously indicated, suggesting a less favorable balance of power on the peninsula. The result was a far more menacing picture of the dangers to American interests in Asia — and especially from China. Reviewing the world situation in September 1951, a CIA assessment concluded: “It seems almost certain that Peiping intends to play an aggressive, expansionist role in the Far East.”

The limited scope of the Korean War made this power outlook particularly problematic for America’s prior plan to maintain low levels of military spending, rely heavily on a small nuclear arsenal, and mobilize the nation for war only if necessary. Whereas the early conception of Cold War containment assumed a geopolitical binary — either peacetime competition or total war — Korea revealed a new category of limited war. Unlike peacetime competition, limited wars required the use of military force in battle, with attendant costs in blood and treasure, not to mention escalation risks. And, unlike total war, limited wars were contained — which meant that the United States had to alter its military strategy to manage escalation, stymying its ability to leverage nuclear weapons or, in cases like Korea, to attack the heart of China’s military effort.

Countering local aggression in the context of limited wars generated a novel set of strategic requirements for the United States. The global balance of power seemed to be at stake, and throughout Asia, the defense of noncommunist areas assumed greater significance as domino-theory logic took hold. Militarily, maintaining the offshore defense line — Japan-Ryukyus-Philippines-Australia and New Zealand — remained critical, as did denying Taiwan to the communists, in order to assure the vulnerability of the Soviet Union’s eastern flank. Yet the Korean War demonstrated that the prewar policy of providing economic and military assistance — in the absence of broader security guarantees — would not forestall the newly salient specter of external aggression by Soviet satellites in strategically vital locations. To buttress deterrence, the United States entered into a succession of mutual defense treaties with the Philippines (August 1951), Japan (September 1951), Australia and New Zealand (September 1951), South Korea (October 1953), and Taiwan (December 1954). The Truman and Eisenhower administrations also accelerated U.S. military assistance to the French in Indochina. This vast array of new alliances was undergirded by extended nuclear deterrence and backed by permanent regional troop deployments, representing a new chapter in the history of American foreign relations.

Such an overseas network of peacetime allies and bases would not come cheaply. After the Korean War began, a new approach to government spending emerged; this shift revealed an unprecedented American willingness to tolerate the costs of military investments in conditions short of general war, as well as the economic capacity to do so. By lifting strict caps, the war inaugurated a military Keynesianism that unshackled defense budgets from spending limits that had previously seemed economically and politically immutable. Despite the Truman administration’s prior insistence on a $13 billion budget cap, the ultimate defense authorization for Fiscal Year 1951 totaled $48.2 billion. Outlays went even higher the following year. Although spending diminished as the war wound down, military spending never again retreated to pre-Korean War levels.

The Korean War’s Lingering Legacy

In his memoirs, President Dwight Eisenhower reflected on the strategic transformation wrought by the Korean War:

In 1953, as the Korean War came to an end, this country … recognized that it could not lay down its sword and shield and return to a peaceful world in which wars would be no more. It faced the fact that it could no longer throw off the burden of budgets for armaments on a wartime scale. It realized now that it must learn to live, possibly for a lifetime or longer, with great arms close at hand, with millions of men in uniform, and with an implacable enemy always just beyond the horizon.

Were it not for the Korean War, the U.S.-Soviet rivalry would still have dominated post-World War II international politics, but the nature of the Cold War might have been quite different. It might have been characterized by competition via measures short of war rather than the limited and proxy wars that peppered the Cold War. Further, the United States might not have embraced the permanent militarization of its foreign policy with an attendant increase in the size of its standing peacetime forces. Without a strategic focus on limited war contingencies, America might not have built alliance and overseas basing networks or established a permanent U.S. forward presence across multiple regions — even NATO, which predated the Korean War, became considerably more institutionalized in response to it. And if U.S. and Chinese forces had not directly clashed on the Korean battlefield, China might not have hardened into an imminent and high-priority danger in the eyes of American policymakers, inaugurating more than two decades of frosty relations.

Crises frequently become critical junctures, all the more so when they occur during moments of strategic flux. In the years following World War II, even as the Iron Curtain had already descended, the nature and objects of Cold War competition between the United States and the Soviet Union were not yet crystalized. Seven decades after the Korean War, the world is experiencing another moment of uncertainty, as new patterns of geopolitical interaction are once again being forged amid significant West-East power shifts, especially China’s ascendance, and the upheaval created by COVID-19. The Korean War’s legacy suggests that policy choices made in response to a crisis can have effects that are far more durable than their architects would have ever imagined.

Given America’s enduring influence over the scope and nature of international cooperation, competition, and conflict, its policy choices will determine the course of 21st-century geopolitics. If Washington adopts a purely reactive approach to the diverse and growing array of crises it faces — from  COVID-19’s domestic and international impacts, to a prospective showdown on the Korean Peninsula and tension between nuclear-armed neighbors along the Indo-Chinese border, with more turmoil likely forthcoming — its efforts will be inadequate and possibly self-defeating. Much of the character of the post-pandemic international order and great-power competition — in Asia and globally — remains undefined. To seize rather than cede the initiative in forging the coming era of geopolitics, the United States must approach each crisis with a clear vision of the future it seeks to create. With lucid crisis management and strategic planning, the United States can shape the field of competition, leverage its comparative advantages, and further its interests despite a burgeoning rivalry with China. Failure to act with purpose and foresight may instead produce a geopolitical contest that proves more combustible, costly, and complex than the Cold War.



Rebecca Lissner is an assistant professor in the Strategic and Operational Research Department at the U.S. Naval War College and is the coauthor with Mira Rapp-Hooper of An Open World: How America Can Win the Contest for Twenty-First-Century Order, which will be published by Yale University Press in September. This article draws on her book project examining the effects of military interventions on American grand strategy. The views expressed here are her own.

Image: Good Free Photos (Photo by Cpl. Peter McDonald)