Role of China
China had gotten involved in the Korean War when General MacArthur had pushed back the northerners, who had been trying to take over the south, back up north and he had made them retreat so far north that they almost went into China. China had practically saved the North Korean communists from complete destruction. After the attack in Inchon, the North Korean Army had been cut off and was disappearing. The Chinese attacked across the border and pushed the UN forces back to the South. They then helped support North Korea for the rest of the war, allowing it to survive.
The role of China was major, if China had not been there to support the North Korean Army, then they would have completely disintegrated. China had supported North Korea because they were both for the communist side, and even though they were tired from the previous wars, they needed one thing, power, manpower. And they hoped they might get help with that while helping and supporting North Korea for the war.