Reasons to why China entered the Korean War:
China entered the Korean War because of a variety of reasons.
The first reason was for self defense, as China was afraid of being attacked militarily and politically, the latter referring to the threat of Anti-Communism.

China, having just become a communist nation, was still relatively unstable politically. Therefore it wanted to keep a 'safety zone' so that no countries, especially the anti-communist nations would disrupt its political reconstruction. Countries that come to close might try to use the opportunity to disrupt the internal security of China and try to overthrow The CCP(Chinese Communist Party) and try to change its ruling system from a communist to a democratic nation. China was afraid that when South Korea won the war and China did not help, the US would have a big opportunity to break into China and try to convert the entire nation into a democratic nation and put the KMT(Kuomintang) back into power. As such, it was willing to lend aid into the war to try and drive the 'evils' of the American imperialism from North Korea.

Also, China did not want to enter the war much later as it would be economically less advantageous as compared to if it had entered the war much earlier. Furthermore, China also wanted to protect its own infrastructures from other countries. For example, the hydro electrical dams built at South Manchuria would have been seriously exploited if the other countries successfully captured the whole of Korea and proceeded onto China
The second reason could be due to General MacArthur's bad decision to not heed the Chinese warnings for the US troops to back off.

General MacArthur, who was invading North Korea, was coming far to close to the Yalu River, the border of China and North Korea. As such, the government of China warned him not to come closer than 20 miles from the Yalu River or China would consider that as a threat to the internal security of China and China would then enter the war on the side of the North Koreans. However, General MacArthur ignored China's warning and continued to march forward, closer and closer to the Yalu River. Despite repeated warnings from the current US president at that time, President Henry Truman, MacArthur continued to push forward and even boasted that the Americans would be able to return home by Christmas. He even provoked the Chinese by lining his men up against the side of the Yalu River.

On October 25 1950, China launched 2 minor skirmishes that routed the American soldiers. Then on first November 1950, the first major battle started when thousands of PVA(People's Volunteer Army) encircled and scattered many of the soldiers and turned the tables of the war, where it begun its offensive push downwards.






























Peng Dehuai, commander-in-chief of the PVA(People's Volunteer Army) during the Korean War


PVA(People's Volunteer Army) crossing the Yalu River


The third reason was a more offensive reason, which was to prove China's military strength.
The communist China hated the Americans as they had backed the KMT(Kuomintang) during the Chinese Civil War and they had been looking for a chance to fight the Americans. Also, Mao wanted to show that China was a force not to be reckoned with and she wanted to show that a country can still be strong with a communist government. Mao also wanted to show that China was a force in world communism as he thought that Russia had looked down on China and entering the Korean War was a good way of showing China's military strength. As such, China entered the war and supplied aid to the North Koreans, just like what the Russians were doing. China entered the war because of national pride and to show to the West that it too, can be a world power.

The last reason was because China felt indebted towards the North Koreans as they had provide them with assistance during the Japanese invasion of China as well as the Civil War in China and as such, helped to establish China as a communist nation by helping the CCP(Chinese Communist Party) to win the war. During the Japanese invasion, Chinese and Korean communists were cooperating with each other to mount guerrilla warfare against the Japanese in a combined effort to drive them out of both Korea and China. During that time, the Chinese and Korean communist leaders, Mao Zedong and Kim both forged close ties with each other. Furthermore, during the Chinese Civil War between the nationalist KMT(Kuomintang) and the communist CCP, (Chinese Communist Party), Kim supported the communist side by continually supplying them with food, supplies and troops.




























Chinese propaganda poster asking the Chinese to stand up help the Koreans while resisting the Americans

In short, the reasons that could have made China enter the Korean War in the side of the North Koreans was because of:
1. National Security
2. MacArthur's Threats towards China
3. To prove China's Military Strength
4. To repay North Korea for all their help towards China


















Chinese anti-American poster

Acknowledgments for the pictures:
http://factsanddetails.com/media/2/20080310-Korean%20war,%20anti%20American.jpg
http://factsanddetails.com/media/2/20080310-Korean%20war,%20anti%20American%202.jpg
http://en.wikipedia.org/wiki/File:General_Peng_Dehuai.jpg
http://images.china.cn/attachement/jpg/site1007/20090820/000bcdb95f1d0bf7609a60.jpg