Why Did The U.S. Enter The Korean War?

The Korean War has been called America's "forgotten war," as The Korean War Legacy Project describes it. Sandwiched between the generation-shaping World War II a few years earlier, and another generation-defining war, the Vietnam War, a few years later, the conflict has gotten relegated to a years-long footnote in the history of American military intervention.

When the smoke had cleared, 40,000 Americans had died, and another 100,000 were injured in the conflict, according to History. Meanwhile, the war ended with the Korean Peninsula being split more or less in half, and to this day, North Korea, helmed by a series of saber-rattling communist dictators, continues to menace its neighbors and the US.

But why did the United States enter the war in the first place? The answer, like history itself, is nuanced, and any narrative that attempts to boil down the causes of the war to their essence is likely to leave out quite a bit. Nevertheless, at the end of the day, the main reason the US entered the war was the same force that informed much of the nation's foreign policy between the late 1940s and late 1980s: communism.

On June 25, 1950, according to History, approximately 75,000 soldiers from the North Korean People's Army breached the 38th parallel that separated North and South Korea, effectively beginning the Korean War.

At the time, according to BBC News, the US adhered to the so-called Truman Doctrine which, according to the U.S. State Department, held that the US should provide support to nations under threat from authoritarian forces. Further, the United States had been keen to see communism contained.

As for the Korean Peninsula specifically, there was a larger matter at hand. The United States also feared the so-called "domino effect" — the fear that if one nation fell to communism, so would another bordering or nearby nation, which would in turn cause another to fall, and so on. That boded ill for the US, since Japan is just a few hundred miles across the ocean from Korea, and Japan, at the time, was becoming one of America's biggest trading partners, according to the BBC. Protecting America's trade role with Japan may have been the biggest reason for the country's entry into the conflict, according to the BBC.