North Korea is sending lots of signals that it's about to start World War III. While there is a real risk that some misstep or miscalculation might accidentally start a conflict, and while it is certainly possible that the country could repeat a smaller-scale attack like its November 2010 shelling of South Korea's Yeonpyeong Island, there are some very good reasons to think that Pyongyang is bluffing about full-scale nuclear war.
Still, it's worth asking: Could North Korea carry out its "U.S. Mainland Strike Plan," apparently detailed on a chart in Kim Jong Un's war room, in which it launches simultaneous missile attacks on Guam, Hawaii and major cities on the West and East coasts? What about its threatened "precision nuclear strikes" against the U.S.?
The short answer is, no, probably not. Let's rule out the nuclear threat right now: while North Korea does have nuclear warheads, it does not appear to have mastered the technology to miniaturize them enough to put on top of a missile.
The odds for non-nuclear missiles aren't much better. James Hardy, the Asia-Pacific editor for military technology publication Jane's Defense Weekly, wrote in a CNN article pointedly titled, "No, North Korea can't hit Hawaii" that "there is little to no chance that it could successfully land a missile on Guam, Hawaii or anywhere else outside the Korean Peninsula that U.S. forces may be stationed."
Let's look at two different kinds of North Korean rockets, the kind we know it can use and the longer-range ones that the country is still developing. North Korea's existing, tested rocket programs can't reach the U.S. They just can't. Here's a map of their ranges, from the Federation of American Scientists and the Center for Nonproliferation Studies, via Foreign Policy:
Those green circles indicate the range of North Korea's existing rocket programs. You'll notice that none of them come remotely close to any part of the U.S., including Guam or Hawaii.
But what about North Korea's experimental rocket programs, such as the Taepodong-2, the range of which is indicated above with a red circle reaching all the way to Alaska? Well, the Taepodong-2 has been tested exactly once, but it failed about 40 seconds after taking off. It appears that this rocket is not yet ready to take off successfully, much less make it all the way across the vast Pacific Ocean.
It is true that North Korea is also developing the Unha-3, a version of which it recently used to launch a single satellite into space. But there are a number of reasons not to worry about the Unha-3 just yet: it was just one successful launch, earlier attempts had failed and all the rocket had to do was break into the atmosphere. Hitting a city, or even a continent, thousands of miles away is a different sort of task requiring a different sort of rocket.
Even if North Korea did decide to start a war against the U.S., or even if a second Korean War begins accidentally, there is very little reason to think that it could carry out any part of its purported battle plans against the U.S. mainland.