Scarcity usually drives up value, but not in the nuclear-bomb business. At the height of the cold war, with tens of thousands of missiles on hair-trigger alert and the world perpetually poised for Armageddon, a stint in the nuclear chain of command was a fast track to military promotion. Now global warhead stockpiles are at their lowest for almost 50 years, and the career-making military action is elsewhere. In a sign of the times President Nicolas Sarkozy vowed last month to trim France's force de frappe to under 300 warheads, half its peak cold-war tally. Keeping the deterrent up but warhead numbers down puts France in line with America, Russia and Britain (see table). Of the five recognised powers, only China is thought still to be adding to its arsenal. But whether it is building up numbers, or just replacing older missiles, is anyone's guess. America and Russia have thus far anchored their weapons cuts in treaties, though they disagree over what should replace the Moscow treaty that will bring each side down to 1,700-2,200 deployed warheads by 2012, and also over future counting rules. Russia had originally suggested a limit of 1,500 by 2012. Others say 1,000 warheads each is easily enough to keep the peace, and for America to extend a nuclear umbrella over its allies. Both keep a lot more warheads in reserve than are officially counted. America is now dismantling some of these more quickly; Russia has a backlog of thousands. Mr Bush is lobbying Congress, so far to no avail, to be allowed to develop a "reliable replacement warhead'