The Korean War
After the Second World War, Korea had been separated in two, to be reunited with an election which never came. The partition between the two was at the 38th parallel where fighting continued to take place throughout the Korean War.
In June of 1950 communist North Korea invaded South Korea. South Korea was not the epitome of democracy, but the United States supported them to uphold containment and stop the spread of communism and create capitalism there. Meanwhile, the Soviet Union supported the North.
North Korea actually got pretty far, making use of weapons and tanks from the Soviet Union and some support from China (though not openly). They even took control of South Korea’s capital, Seoul. But then a United Nations (UN) backed invasion by Douglas MacArthur pushed back the North Koreans. They continued, pushing further than the UN had originally said, getting all the way to the border with Red China. However, there were people ready in China to help North Korea and together they repelled MacArthur’s forces back to the 38th parallel. Then there was a stalemate.
During the Korean War, the Chinese and the Soviets, unlike the Americans, had the ability to use their early-warning radar. They were able to appear out of nowhere and descend on the United States Air Force (USAF). The USAF did have the advantage of radar gunsights on their side, however.
Eventually, a cease fire was signed on July 27, 1953 though south Korea never did sign it. The United States saw this conflict as proof of the need for NSC 68 and that communism was spreading across the world.