the americans decided that an armed resistance was necessary and they went to the united nations, shades of bosnia here, they went to the united nations to get support and, as luck would have it, the soviets were sulking, this was quite common in the nineteen forties and fifties, and the a the soviet ambassador to the u n was having a sulk and was refusing to attend the security council and he therefore persuaded the security council to pass a resolution er producing a united nations force to aid plucky little south korea against its vicious oppressive northern neighbours  and so the korean war started and the united nations' forces were commanded by one general douglas macarthur, general douglas macarthur, in case you don't know, won the second world war single handedly