While most of the world's attention is on Iraq and to a lesser extent Afghanistan, the big problem child that may determine just how ugly the 21st century is is Pakistan, where President/General Pervez Musharraf is facing a crisis. Musharraf came to power via a coup in 1999 and has been a key factor in the war thanks to his ISI's influence over the Taliban in the years leading up to the September 11 attacks and how willing he has and has not been to deal with terrorists in and around Pakistan.
Musharraf has become increasingly unpopular in a nation where the U.S. isn't particularly well-regarded, and his latest move, removing a Supreme Court Justice for unspecified abuses of his authority has done little to make him any more popular. And while it would not break my heart to see Pakistan return to a more republican system of government, Pakistan is the only nation on Earth right now that combines an Islamic-majority population and nuclear weapons, a combination that could theoretically be unfortunate, to say the least.
On the other hand, as Iran continues to pursue its own nuclear development program, it is clear that the relatively limited nuclear club is going to expand to other Islamic nations sometime in the next 10-20 years. Pakistan may well be the canary in the coal mine, showing us where that development will lead.
It is my opinion that, while a Pakistan dominated by Islamic extremists would not be a good thing, it is unlikely it would lead to the use of nuclear weapons, either by Pakistan or by an Islamic terrorist group. The risks of massive retaliation are too great for any but a madman to take the chance by handing a bomb over to someone willing to use it against a Western city. Still, while the chances of that occurring are slim, they are not zero. What happens in Pakistan over the next few years should provide a good testbed for seeing how other nations may act as they join the nuclear club, assuming that Musharraf will have to relinquish power at some point in those years.
While the West cannot and should not try to influence this process directly, there are things they can do to make the transition as risk-free as possible. A good start would be ending the habit Western powers have of treating third world nations as children. While Europe at least has the excuse of having been colonial powers for centuries, even the U.S. has a bad habit of telling other nations what is in their best interests and what they should or should not be doing, a recipe for resentment and pushback. The West would be far wiser to treat all third world nations like relative equals worthy of respect.
The 21st century is going to see the continued advance of technology, including technologies capable of greater and greater destruction. Since nations will acquire this technology sooner or later no matter what the West does to try and stop them, the only logical answer to this problem is changing how the international system operates to give smaller nations incentives to use it rather than violence to achieve their goals. Pakistan is a good testbed for working out these strategies before they're absolutely necessary.