In 1952 the U.S. government decided to invade Korea because the Koreans of the north did not want Koreans of the south agree to the U.S. dictating their form of government. The American believed, since it won WW2 in Pacific they can do as they see fit. So the U.S. inserted itself into Korean post-war affairs, fought the Korea War and killed 3 million Koreans, most of them in the north. The war stopped in a stalemate in 1954, both sides took heavy losses. China also fought U.S. as it began to invade China, extracting a big defeat. After 1954 the north proceeded to form its own country and vowed to extract revenge on the Americans who killed 3 million of them in a carpet bombing heavier than that on Nazi Germany and Tokyo.

No matter what will happen, you can count on NK an enemy of the U.S. for another century.  The U.S. reserved its most bloody wars on the Asians. The Philippines, the Japanese, the Koreans, the Chinese, the Vietnamese, and Cambodians. They don't forget. Ever!