"We have evened the account with India," said Nawaz Sharif, the Pakistani prime minister. That simple statement explains why the pleas from Bill Clinton and Tony Blair for Pakistan to show restraint fell on deaf ears. But evening the account does not mean closing it. It means that both sides have reached an enhanced state of readiness for nuclear war: what matters now is the stability of the stand-off between India and Pakistan.
The trouble is that as more and more countries possess nuclear weapons, the greater the chance that, one day, someone somewhere will press a button with terrible consequences. However, the only practical way to minimise that danger is to proceed step by negotiated step to build up the international apparatus of treaties and arms control inspection.
The tests of recent weeks will have two contradictory effects: on the one hand, they will spur both countries to build up their military strength, but, on the other, they make it easier for both countries to sign the international treaties to ban further tests and to prevent the spread of nuclear weapons technology still further. Pakistan has always offered to sign if India will and, to that extent, Mr Sharif's talk of "evening of the account" offers hope that a plateau of mutual deterrence has been reached.