In Pakistan's Swat Valley on Sunday, militant Islamist leader Sufi Mohammed bluntly defied the country's secular government and its system of laws. As to its democratic institutions, he said, "supporting an infidel system is a great sin," and he laid out a plan to bring "a complete Islamic system" to Pakistan. Such Taliban-style militants are assuming control in Pakistan's northwest provinces, openly promising to take over the rest of the country. Despite brutal enforcement of Islamic law, the secular government seems powerless against determined radicals exploiting poverty, class hatreds and decades of corruption. The US has vital interests in a region where both Pakistan and India have nuclear arms. We hear mounting concern about instability with international consequences.