the last time the us fought china in a war, the chinese military put the 8th army into the longest and bloodiest retreat in u.s. history, china encircled and completely annihilated multiple brigade-sized formations, and was able to sustain a war of attrition against the us for years until america decided to give up and let china have half of korea. it was so bad that the us never even dared to try and invade north vietnam because they were terrified of chinese intervention into that war.
United States