North Korea says it wants to conduct one or two more nuclear tests this year in order to force the United States into diplomatic talks—by doing the exact opposite of what the United States wants them to. Since the nuclear test they conducted on Tuesday brought near universal condemnations and rumblings of new Security Council sanctions, Pyongyang has apparently decided that the best course of action is to become even more belligerent until the Americans give in and come back to the negotiating table.
The only flaw in that strategy is that the United States has spent the last decade doing everything it can to avoid direct negotiation, usually by pointing out (correctly) that such a move would be rewarding Pyongyang's terrible behavior. U.S. officials did call on North Korea to "refrain from additional provocative actions" after Friday's report that Pyongyang had informed Beijing of the new test planning. But North Korea already broke one major peace agreement, and American diplomats are not interested in being played for fools twice. (That's one reason they insist on the six-party talks, so the responsibility for any future agreements are equally shared.)
North Korea has consistently said they want direct, bilateral talks with Washington, including a new treatyto formally end the Korean War, but both George W. Bush and Barack Obama have held the line by insisting that the other side give up their nuclear weapons first, and then they'll talk. North Korea has responded by conducting more tests, building more rockets, and issuing more threats. If the end goal was peace, that hasn't helped matters in the slightest.