President Bush's decision to withdraw from the 1972 Anti Ballistic Missile Treaty (ABM) will take effect in six months time. In the shorter term, it will place serious pressure on the coalition painstakingly built by his Secretary of State, Mr Colin Powell, in the aftermath of the murderous events of September 11th.
Just three months ago, the civilised world shared America's grief to the extent that it was prepared, with few reservations, to join its campaign against international terrorism. The United States, for its part, moved away from a disturbingly unilateralist path which had seen it opt out of a string of major international pacts including the Kyoto protocol on the environment.
The emphasis shifted to coalition building. Russia, admittedly with its own interests in mind, joined America's more traditional allies in the response to the appalling attacks on the World Trade Centre and the Pentagon. Initially, its considerable influence was brought to bear on the former Soviet republics of Tajikistan and Uzbekistan, which share frontiers with Afghanistan, and later it sent an armed detachment into the centre of Kabul.
Mr Bush has chosen to abandon ABM at a time when the war in Afghanistan has strengthened his support both in the United States and abroad. His move has been described in Washington as a political master stroke. It may, on the other hand, mark the start of a major erosion of the international support engendered by September 11th. The war is now entering its successful end-game and, under these circumstances, it is difficult to avoid the conclusion that a decision has been taken to abandon a coalition that is no longer needed.
This case will be put quite strongly in Russia by opponents of President Putin who wish to brand him as an American puppet. Mr Putin will also be under pressure from a military lobby which is already talking in terms of abandoning the Strategic Arms Reduction (START) treaties and augmenting a nuclear arsenal which is capable of destroying the planet several times over.
In China, the temptation for nuclear re-armament will be stronger. When Mr Bush, by ditching ABM, goes ahead with his missile defence programme - dubbed as "Star Wars Two" - Beijing may feel it necessary to redress the balance by increasing its arsenal. Closer to the current centre of conflict, the removal of ABM could encourage Pakistan and India to increase their nuclear capabilities.