Earlier quoted context omitted.
America was in almost no way the aggressor. North Korea Invades South Korea on June 25th 1950. The UN, for probably the first,last, and only time, takes military action (at American behest and because the Russian's were boycotting the UN) led by a US General and primarily American troops. This force and the South Korean Army repel the North Koreans and drive into North Korea (which was suppose to hold open elections…
Nobody has explained to me why Korea was even divided up into the North and South in the first place. It should have been left to its own devices after the Japanese empire collapsed at the end of WW2. That is, the US/UN shouldn't have been occupying the South and the USSR/China shouldn't have been occupying the North. Seems to me that the fault should be assigned to all of those countries/organizations.
Some countries were split into occupation zones between the Western allies and the Soviets. Germany was one. There were four occupation zones: British, American, French, and Soviet. The intention was for a new German government to be formed that would govern all four zones, but negotiations broke down and the Soviet occupied zone formed one government (German Democratic Republic, known as East Germany) and the Western occupied zones formed another (Federal Republic of Germany). This state of affairs continued until the fall of communism, when the East Germans more or less decided to join the Federal Republic giving us today's Germany.
Korea was a similar case. There was no Korean government--it was a Japanese possession since 1910--so, with the intent of punishing Japan and giving the Korean people self-determination, it was temporarily occupied by the Allies until they could set up a democratic government. It was partitioned between the Soviets and the Americans, who, as in Germany, formed opposing governments. And then the North invaded the South--and that's where the war began.