Two factors define the North Korea we see today. The first is the dreadful bombing unleashed upon it by the United States and its allies during the 1950-53 Korean War — a war that in many Korean eyes was a far from illegitimate attempt to unite a nation arbitrarily divided into north and south in 1945 after liberation from Japanese control. As one Australian pilot put it to me after that war, "we bombed all the farmhouses, then we bombed the cows, and when we ran out of cows we bombed the haystacks." The bitterness of anti-U.S. feeling that comes from those years cannot be underestimated.
The second factor was the 1994 Agreed Framework with the U.S. So as never again to be powerless before overwhelming U.S. air power, North Korea in the '90s had set out to build a plutonium reactor to produce its own nuclear weapon. But the U.S. intervened.
Literally hours before a planned U.S. air attack on the reactor former U.S. President Jimmy Carter negotiated on behalf of the Clinton administration an Agreed Framework under which the U.S. and its allies would assist in building a light-water reactor to replace the offending plutonium reactor (the KEDO project). Promises of economic aid and diplomatic recognition were included.