Nuclear attack is the biggest military threat to the security of the United States. A single megaton-size nuclear warhead aimed at a major American city could kill or maim over a million people. A handful of nuclear weapons aimed at several cities could collapse the national economy.
It is widely believed that a stable deterrence relationship exists between the U.S. and the other two major nuclear powers, Russia and China. North Korea, however, is not part of that relationship and it has recently tested missiles capable of reaching U.S. territory. Intelligence reports indicate the North Korean regime is working to wed nuclear warheads to its long-range missiles.
Iran may follow, with similarly unpredictable consequences. And even in the case of Russia and China, there is the danger of accidental or unauthorized launch of intercontinental ballistic missiles.