Why Does Everyone Try to Change Korea's History?

My wife was complaining about the Chinese Netizens and their accusations that Korea was distorting history in the Jumong (주몽) drama. She was wondering why everyone like Japan and China wanted to change Korea’s history. I then asked her what Koreans think about the U.S. and our involvement here. In Korean I said, “한국 교과서에서 육이오 전쟁에 대해 이야기하면 미국이 도와주러 온다고 하지 않고 UN만 왔다고 되어 있다.” (In Korean history books when it talks about the Korean War, it doesn’t mention that the U.S. came to help, but rather just says the U.N. came.) She looked at me and said “of course! The U.S. didn’t come to help, they came for their own benefit. They would have taken over South Korea as their own colony if the Chinese didn’t help them.” What do you say to that? I went through some of the history and errors in her logic, and then she commented she needed to read more history books. I will just need to make sure they are not Korean history books, or this conversation will take place again…