role of china
When US/UN forces began to push North Korean forces back during the Korean War, General MacArthur, in his typical careless manner, kept pushing the North Koreans further and further back, even though his Commander-In-Chief, President Truman, told him not to. As US/UN forces got closer to China, they felt they had to react or there would be US forces directly on their border (which was exactly what Truman was worried about), so about a million screaming Chinamen came swarming across the border to push US/UN forces back, which ended up protracting the war even longer.
MacArthur felt that the North Korean army had been essentially destroyed by the middle of October, and, against the recommendations of the Joint Chiefs of Staff, he sent his forces into the northernmost parts of North Korea. His troops were hit by surprise and decimated when Chinese Communists troops began attacking his forces. On October 25, the PRC made an attack on ROK soldiers and routed them at Pukchin. On November 1, the Chinese defeated American troops at Unsan, in the first Chinese-American combat of the war. When MacArthur tried to order bombing raids against some bridges near the Manchurian border, Truman and the JCS delayed the bombings out of fear that errant bombs might land in Manchuria. On November 7, a US Congressional Election was held, which, although it preserved the Democratic Party majority, was viewed by many as a referendum criticizing Truman's Korean War policy.
MacArthur felt that the North Korean army had been essentially destroyed by the middle of October, and, against the recommendations of the Joint Chiefs of Staff, he sent his forces into the northernmost parts of North Korea. His troops were hit by surprise and decimated when Chinese Communists troops began attacking his forces. On October 25, the PRC made an attack on ROK soldiers and routed them at Pukchin. On November 1, the Chinese defeated American troops at Unsan, in the first Chinese-American combat of the war. When MacArthur tried to order bombing raids against some bridges near the Manchurian border, Truman and the JCS delayed the bombings out of fear that errant bombs might land in Manchuria. On November 7, a US Congressional Election was held, which, although it preserved the Democratic Party majority, was viewed by many as a referendum criticizing Truman's Korean War policy.
implications
I personally think that if General Douglas MacArthur did not force his troops into North Korea, China would not have gotten as much involved with UN/US because China is an ally of North Korea. Also, without the involvement of China, NK would've lost the war and would have probably surrendered. China's was crucial for the survival of NK.