Many sources argue that President Harry Truman went into Korea to prevent the conquest of an independent nation by the communist North. His motivations stemmed from the urge to resist the advancing tide of the Soviet Union and, by extension, communism. The perceptions associated with losing Korea would have certainly affected American diplomatic efforts and cast doubt upon US deterrence elsewhere, but it wouldn't have affected American power or wider strategic goals. Korea was not considered an "industrial strongpoint" (as outlined by George Kennan).

How then do political Realists explain American intervention on the Peninsula in 1950?

  • 1
    How is that not the explanation for the intervention?
    – Joe W
    Mar 17 at 1:44
  • @JoeW That is not a realist explanation.
    – aengel
    Mar 17 at 2:04
  • 4
    How is it not a realist explanation? Just because you don't think something would have impacted the grand strategy at large doesn't mean it isn't a realist explanation.
    – Joe W
    Mar 17 at 2:30
  • 6
    Indeed, it is not enough to merely point to grand strategy. The US may have intervened for tactical or operational reasons, rather than strategic reasons. Also, I quite frankly do not know what the definition of a "political realist" is in this context. I have only ever heard that phrase used to mean "someone who agrees with me" - but I'm sure you can answer that question yourself, so you must mean something else.
    – Kevin
    Mar 17 at 3:00

2 Answers 2


Note that in 1950, when the war started, political realists like Kennen were already critical of a pure military solution.

For example, Hans Morgenthau had this to say on USA motivations in this 1962 article, where he compares Vietnam (which was at the time split between North and South, but not yet at war) and Korea:

It was then [during the First Indochina War - 1946-1954, so exactly during the relevant period] widely held that the acquisition by a Communist power of any piece of territory, regardless of its size and location, was a calamity which signaled the beginning of the end for the free world. Vietnam, for instance, was considered to be the “cork in the bottle,” the “first in a row of dominoes”; if it fell all of Indochina would fall, too.

By analogy, Korea in 1950 would be a "falling domino", and stopping the process was seen as important for stemming the spread of communism in the region - to Japan, for example. Realists saw this viewpoint as a misjudgement of situation:

In fact, of course, North Vietnam went Communist, but South Vietnam did not, nor did the other states of Indochina. This unexpectedly favorable outcome of the Indochina war provides empirical proof for the proposition that Communist territorial gains can be localized and affect the interests of the United States adversely in differing degrees.

First Indochina War ended with the signing of 1954 Geneva agreements. In other words, realists saw USA strategy of direct military countermeasures as costly and ill-advised, and proposed adhering to diplomatic solutions based on multilateral agreements, if the territory ceded would not bring significant change to balance between blocks (in other words, ceding half of Germany was bad, because it gave Communists industrial strength, but ceding half of Vietnam or Korea was acceptable; realists would frown of former, but were all for latter). As such, they saw American intervention on the Peninsula in 1950 as a mistake driven by an overly-rigid "no step back" policy.

  • +1 But falling domino theory still seems to me like a very subjective belief (even if a bit more solid than prestige and credibility in the other answer) - is this really how politicians make decisions about lives and deaths of thousands? Mar 17 at 9:54
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    @RogerVadim Communism still was a relatively new thing in 1950s, and predicting how it would fare in long run wasn't easy; yet it was a pressing matter, because in only ~30 years the communist bloc managed to considerably grow its power. So I wouldn't call this particular decision exceptionally subjective. Mar 17 at 11:17
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    @RogerVadim 1. Humanity is a lousy study subject - changes quicker than you can gather information, actively conceals information about itself. Lousy researcher, too -biased and prone to data manipulation; 2. strategy is a game with incomplete information, you will have to make decision using intuition at some point; 3. Political science is too politicized (heh) to have the kind of community consensus exact sciences have. But Sun Tzu's book is a pretty good summary of basics, I think. Mar 17 at 13:24
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    Could be wrong but domino doctrine came up after Korea, IIRC. So talking about it in 1962 does not enlighten as to motivations in 1950. However, containment was already a thing. Mar 17 at 16:32
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    @ItalianPhilosophers4Monica well, the principal thought that communism will spread in a chain reaction if left unchecked was definitely present in Truman's reasoning when military aid to Greece and Turkey was offered. Eisenhower was probably just the first who managed to put a good, memorable label on the concept. Mar 17 at 17:02

TLDR summary; two views basically, both claimed to be realist:

  • it was a mistake according to Morgenthau, Kennan etc. Korea not a "core interest" basically. Realists never claim all countries act according to realism, but admit temporary ideological follies are possible.

  • it wasn't a mistake because the goal was to diminish the prestige and credibility of the Communist camp by showing they couldn't easily take a province in their near abroad. E.g. Benjamin Miller or Jeffrey W. Taliaferro. Actually the latter's theory is more descriptive than prescriptive, since it includes loss aversion borrowed form prospect theory, as a factor, so has a "mistake factor" added, essentially.

Depends whom is your favorite realist, I suppose. Since there's already an answer from the Morgenthau perspective... I'll only say about that one thing to keep in mind is that, generally speaking, no realist claims their theory is always followed. E.g.

Mearsheimer acknowledges that “omitted factors” such as ideology “occasionally dominate a state’s decision-making process” and explains that these exceptions merely demonstrate that there’s a “price to pay for simplifying reality” into theory.

Thus you can have those like Morgenthau who don't explain it through their theory proper, but merely as (random?) deviation from it, as a mistake, ideological folly, etc.

I did manage to find one book chapter by Israeli professor Benjamin Miller claiming that the US deploying to Korea in the 1950, was not a folly or mistake, but precisely what offensive realism demanded them to do. Here's a quote:

Contrary to Mearsheimer, Layne, and Dueck, we argue that US strategy changed twice in the first formative years of the Cold War. In 1945– 46, the US followed a liberal strategy (albeit defensive rather than offensive), but in the 1947– 50 period it switched to a more hard- line defensive realist one. Then, following the North Korean attack on South Korea in 1950, its grand strategy changed once more—this time to an offensive realist one. None of the three studies discussed above captures these variations because they all regard US grand strategy in this period as constant and unchanging.

In addition, in contrast to Layne’s and Dueck’s interpretation, we argue that the main causes for the adoption of these various strategies were not domestic or ideological, but rather external, more specifically, the realization of the military might of the Soviet Union (its control of Eastern Europe and its ability to occupy the rest of Europe) and its rising threat (as deduced by the US decision makers from aggressive and expansionist Soviet behavior). The combined effect of Soviet power and high threat led to the ultimate adoption of offensive realism as the grand strategy that guided the US throughout the 1950s and early 1960s.

So, they argue that the US intervention in the Korean war was realist purely from a non-ideological perspective, simply because of the perceived Soviet threat. Morgenthau, of course, argued the opposite. In fact that book even summarizes the dispute in the realist camp:

It was only later in the Cold War that these realists, whom we call here defensive realists, began to drift away from the consensus urging greater US intervention to limit the Soviet sphere— Lippmann in his famous dissent from Kennan’s Mr. X article, Kennan from what he considered the misinterpretation of his containment doctrine, and Morgenthau even later, concerning Vietnam. Meanwhile, other realists— whom we see as offensive realists— like Dean Acheson and Paul Nitze believed that they were following Walter Lippmann’s realist principle of balancing goals with the power available by expanding American and European military power to achieve the necessary goal of preventing communist expansion into the rest of the world. For many years, then, the realist school was divided between “hard” (or offensive) realists, who advocated increasing Western military power to achieve their desired goals, and “soft” or “restrained” (or defensive) realists who advised the United States to reduce its goals to match its available power.


In Kennan’s view, however, maintaining a balance of power (and thus to safeguard diversity) required only to deny centers of industrial- military capability from the Soviet Union, which means in practice that it was necessary only to defend selected strong points. In contrast, NSC 68 called for the expansion of interests, while taking into account also considerations of prestige and credibility [...] Changes in the balance of power could occur not only as a result of military or economic actions, but from intimidation, humiliation, or even loss of credibility. [...]

The threat defines the interests: Expansion of interests according to the Soviet threat. US interests couldn’t be defined apart from the Soviet threat to them; “frustrating the Soviet design” became an end in itself, not a means to a larger end.

Basically, showing that the Communist camp couldn't achieve a trifling victory in their near abroad of Korea, fit in that vision. (Later repeated in Afghanistan '79, by the way, albeit by different means.)

As discussed elsewhere in that book, it's also worth noting that Kennan opposed the establishment of NATO, which he saw as "enhancing the security dilemma by encircling the Soviet Union with military alliances", so his softer approach to the Communist camp was broader than just Korea.

Finally, realists squabble over what strategy is to be called what, e.g.

Although Mearsheimer is considered the leading offensive realist, in fact his theory with regard to US intervention in the Cold War is not different from defensive realism because it conceives of US behavior as balancing and not defeating the Soviets.

This is somewhat aside, but since someone [not the OP] in comments to the other answer appears interested in prospect theory in political decision making... There's is one paper by Jeffrey W. Taliaferro that combines that with defensive realism to produce what they call balance-of-risk theory. Ultimately it posits that:

Officials initiate risky diplomatic and/or military intervention strategies to avoid perceived losses. Leaders then persevere and even escalate failing peripheral interventions to recoup their past losses. [...] These tendencies produce policies that are driven by concerns about power and security but are at odds with many variants of political realism.

They illustrate that with the USSR in Afghanistan, US (and France) in Vietnam as prime examples, but don't really say anything definitive about Korea, other than that back the US considered itself in a "much stronger position vis-à-vis the Soviet Union in 1954 than it had been in 1950", which is kinda left hanging: no conclusion is drawn about anything else relating to the Korean war.

But interestingly enough such a paper does even talk about prestige being involved in the decisions to fight in the periphery:

The definition of risk offered here focuses on the potential for loss or gain. Depending on the situation, losses and gains generally entail objective measures of a state’s capabilities, such as military forces and equipment, territory, economic resources, and ability to absorb military and civilian casualties. They can also involve subjective items of value that play a role in leaders’ calculations, such as a great power’s reputation for resolve, the credibility of commitments, and prestige. [...]

Senior officials are acutely sensitive to the relative distribution of power and prestige among the great powers. All else being equal, the greater a state’s aggregate power—population, industrial resources, territory, military capabilities, and technological resources—the greater a potential threat it can pose to others. A closely related factor is prestige, a state’s reputation for having material capabilities or status and using those commodities to achieve its desired aims. The ultimate determinant of prestige is victory in a major (or hegemonic) war. The actual task of assessing relative power and prestige, however, is complicated. The various measurements upon which leaders rely are often imperfect.

It's basically implied but not said explicitly that victory in a minor, peripheric war counts for less than victory in a major war, in terms of prestige. Meh, rather obvious.

I see that the author of that paper even wrote an entire book on the topic, and in the table of contents of the latter they do have a full chapter about the Korean war, well, at least until 1951. In [not so short] summary, the author says:

I argue that loss aversion caused the Truman administration to reverse its long-established policy and intervene in the Korean War in June 1950. Officials' perceptions of relative power trends influenced the selection of an expectation level, which in this case was the preservation of the territorial status quo. In 1949-50, a series of adverse developments the Communist victory in the Chinese civil war, the Sino-Soviet alliance, and the Soviet atomic bomb-produced a profound sense of vulnerability among decision makers. Failure to check the projected growth of the Soviet bloc's power would result in the steady of erosion of American power and influence by the mid-1950s. However, if the administration took immediate steps to reverse this trend-mainly through increased defense spending and stronger military ties to Western Europe and Japan-the United States would remain preponderant. In the meantime, however, Truman and his advisors concluded that major war during the American window of strategic vulnerability (1950-53) would be disastrous. Consequently, they sought to avoid any action that might precipitate a direct superpower confrontation, while reaffirming the priority of European defense and the defensive perimeter in the Pacific consisting of Japan, the Ryukus, and the Philippines.

The North Korean invasion represented a dramatic challenge to the status quo. As balance-of-risk theory would expect, Truman and his advisors adopted the risky strategy of committing troops to defend South Korea, a country that officials deemed "strategically insignificant" weeks earlier. Intervention was riskier than other options, given the strength of the U.S. armed forces in June 1950 and the possibly that the invasion was a diversion. Once American troops crossed the Thirty-eighth Parallel in early October, Truman and his advisors sought to recover the sunk costs of their previous policies. They were insensitive to the marginal costs associated with MacArthur's offensive-namely the increasing likelihood that China would enter the war. After the Chinese counteroffensive sent American and allied forces reeling in November and December 1950, the administration opted to wage a limited war, despite widespread calls at home for a unilateral withdrawal and calls from the allies for an immediate negotiated settlement.

Offensive realism suggests that increased relative power and international opportunity drove the 1950-51 Korean War decisions. The theory does explain the escalation of American war aims from containment to rollback in August-September 1950. The retreat of the North Korean army, the diminished likelihood of Soviet intervention, and China's perceived military weakness, gave the administration a window to reunify the Korea at a low cost. Offensive realism, however, does not explain the officials' intervention decision in June and their subsequent refusal to halt the Yalu offensive despite the increasing likelihood of a Chinese counteroffensive.

[...] Truman announced the end of the American nuclear monopoly on 23 September [1949]. [...] The administration faced additional setbacks, including the flight of Chiang and the KMT army to Taiwan, Mao's proclamation of the People's Republic of China (PRC) on 1 October 1949, and the conclusion of the Sino-Soviet alliance treaty on 14 February 1950.

The CIA warned the "West now lagged behind the USSR in terms of total gain of political, economic and military strength."

[...] as balance-of-risk theory would expect, NSC-68 reaffirmed the necessity of maintaining the territorial status quo during the window of vulnerability. After the proposed military buildup, the United States would have the capabilities to "induce a contraction of the Kremlin's power and influence." In the short-term, however, NSC-68 and related documents reaffirmed the defensive perimeter strategy in the Pacific. [...]

The setbacks of the previous months made the Truman administration sensitive to any further deterioration in relative power and credibility. The North Korean invasion on 25 June 1950 came as a complete shock [...]

officials simply assumed that the North Korean invasion was part of a coordinated campaign of Soviet-backed aggression or subversion. Stalin had likely intended the invasion as a diversion for a Soviet move elsewhere or a probe of American resolve. [...]

On 25 June, Truman told his aide George Elsey that "Korea is the Greece of the Far East. If we are tough enough now, if we stand up to them [that is, the Soviets] like we did in Greece three years ago, they won't take any steps."

And yeah a version of domino theory was posited even back then:

On 27 June, the president met with the congressional leadership at the White House. Truman said that he and advisors unquestionably believed that "if we let Korea down, the Soviets will keep right on going and swallow up one piece of Asia after another .... If we were to let Asia go, the Near East would collapse and no telling what would happen in Europe."

At the 28 June NSC meeting, Acheson stated that the deployment of ground and naval forces did not necessarily constitute "a decision to engage in a major war with the Soviet Union if Soviet forces intervene in Korea." However, he observed: "The decision regarding Korea ... was undertaken in the full realization of a risk of war with the Soviet Union."

[...] The 25-30 June intervention decisions support balance-of-risk theory. Truman and other officials considered four options: (1) the continuation of existing policies, (2) the use of airpower to provide cover for retreating South Korean troops and the deployment of the Seventh Fleet to the Taiwan Straits, (3) the use of airpower above the Thirty-eighth Parallel to disrupt North Korean supply lines, and (4) full-scale intervention by ground, naval, and air forces to reverse the North Korean invasion. The administration quickly abandoned the first option and then pursued the remaining three in succession. No option was completely free of risk and each entailed difficult trade-offs. However, given the administration's oft-stated desire to avoid an entrapment in an East Asian ground war or a confrontation with the Soviets in the near term, the two latter options entailed high risks. As the theory expects, officials pursued risk-acceptant intervention options in the periphery as a means to avoid perceived losses to reputation for resolve and relative power.

So yeah, although this was written some 15 years before Miller's book, and the latter doesn't cite it much, it kinda draws the same conclusion that it was a two-phase thing: defensive realism (albeit +loss aversion) that led to the later offensive realism phase, past the 38th parallel.

I'm not gonna paste much of the rest of the analysis here (you're only formally asking about the initial decision anyway), but they do say that the apparently weak Soviet response (elsewhere) and the perception that China wasn't even remotely ready to intervene with troops (CIA assements) led to the transition to the offensive [realism] phase, which is classically explained by a perception of weakness in the enemy camp.

So, yeah, this is also perhaps a good case study in the relative strengths and failings of various realist theories in explaining a sequence of events in the same theatre. OTOH, the author claims that after signs of the Chinese intervention appeared, loss aversion kicked in again [this time relative to having "acquired" in their minds the whole of Korea already], distorting US decision makers thinking back into a situation best explained by balance-of-risk theory (i.e. more like a defensive realism again).

  • Thank you for this thoughtful response. However, I would push back slightly and say that Realism is a descriptive theory, not a normative one (i.e., it claims to be reflective of political realities). Therefore, Realism should be able to explain any political situation through its explanatory lens. While theorists recognise that in practice, this is an impossible goal, realism should technically have an explanation for Korean intervention. I suppose the answer lies in the perceived threat of Soviet expansion...
    – aengel
    Mar 17 at 14:11
  • @aengel: You make a fair point, and more by a lucky coincidence, I discovered a [partly] realism-based take on that war that is much more descriptive (see rather large edit[s]). The tug of war between realism descriptivists and prescriptivists is another interesting aspect, but I'm not gonna get much into that here.
    – Fizz
    Mar 17 at 20:05

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