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 treaty to 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.
That would lead to two possible conclusions. One: Kim Jong-un (and the power base built by his father) are terrible at negotiating. If they really wanted a peace treaty and no sanctions, they could have them tomorrow by turning over their nuclear weapons, opening up all of their country to inspections, and quitting it with the shooting of things at Japan and South Korea. They might honestly believe that increased strength and a lack of fear will bring the U.S. to its senses and the negotiating table, but their actions so far have only pushed them further apart—and even irritated their "ally" in China.
Which makes Option Two more likely: North Korea has zero interest in talking to the United States about anything. The path to Option One is so obvious that it defies belief that they can't see it. It seems much more likely that their actual goal is to keeping doing what they're doing until, at the very least, they acquire a function nuclear weapon. And if they can spin that approach as both a ploy for peace and a brave defiance of the American bullies, that's just a bonus.
The United States will likely respond to this new threat by suggesting that North Korea underestimates American determination—Obama in his State of the Union said that "we stand by our allies, strengthen our own missile defense, and lead the world in taking firm action in response to these threats." It seems more likely that North Korea understands American determination just fine, and so they're just counting on us to continue ignoring the demands they don't really want met.