The link you posted says "elections were scheduled, the Soviet Union refused to cooperate with United Nations plans to hold general and free elections in the two Koreas, and as a result, a Communist state was permanently established under Soviet auspices in the north"

The early events between the Soviet Union and the United States lead to the 38th parallel boundary, and subsequent events. The fact you had 2 Koreas lead to this separation. Yes the people of Korea have a big involvement in that, but democracy doesn't work in all countries everywhere like it does in the United States. Americans need to start considering the differences of peoples and see what works best for them, not push only your ideals because you think it's good for you.