The new U.S. global force posture President Bush announced on Monday will strengthen our military, invigorate U.S. alliances and improve the lives of our military personnel.

Our new posture will allow us to deploy capable forces rapidly anywhere in the world on short notice. It will push more military capability forward, while shifting 60,000 to 70,000 service members from foreign to U.S. bases. It will create a lighter U.S. "footprint" abroad, consolidate scattered facilities, remedy irritants in our relations with host nations, and, in numerous ways, make it easier for the United States to work well with allies and friends on military operations -- to train and operate, to develop military doctrine and tactics, and to exploit new military technologies with them.

The new posture acknowledges (finally) that the Cold War has ended. It anticipates the emergence of new threats. It recognizes new strategic facts, including the entry of former Warsaw Pact nations into NATO. And it capitalizes on new technologies.

During the Cold War, it was assumed that our forces stationed abroad would fight where they were based. We no longer assume that. We cannot know precisely where our forces may have to operate, so they must be agile enough -- light and rapidly deployable -- to be "surged" anywhere on short notice. Flexible and fast forces can more easily succeed in combat, and they can help prevent problems from becoming crises and crises from becoming wars.

The current U.S. posture, a legacy of World War II and the Korean War, has many of the wrong types of forces in the wrong places and therefore acts as a costly drag on American and allied capability. It would be a victory for inertia over strategic rationality to keep two U.S. heavy divisions stationed in Germany, for example, to counter a Red Army attack that happily, more than a dozen years ago, ceased to be a threat.

The heavy forces being redeployed out of Europe will make way for lighter, more rapidly deployable, more technologically advanced forces. As our allies know, trimmer forces do not necessarily translate into less combat power. On the contrary, relatively small forces equipped, for example, with the latest precision-guided munitions can now pack an enhanced punch: Witness the major combat of Operation Iraqi Freedom last year.

The changes in U.S. deployments in East Asia also have a compelling rationale. South Korea, for example, has burgeoned over the past 50 years. Thanks in part to our alliance, it is a strong, democratic and wealthy power, a far more capable ally than it was during and just after the Korean War. To bolster deterrence and keep our alliance vital, we are updating the allocation of responsibilities. We are plucking a thorn out of South Korea's flesh by moving a U.S. headquarters out of downtown Seoul. We are shifting U.S. forces southward on the Korean Peninsula, beyond the range of North Korean artillery, and consolidating them efficiently into hubs. We are increasing our naval and air power in the region and moving high-tech ground capability to South Korea.

All of this means we will have greater capability to deal with threats in the region, from North Korea or anyone else, even as we shift some troops from Korea back home. Our Korean allies appreciate the wisdom of updating our arrangements. They know it is the key to sustaining the alliance for the next 50 years.

In this political season, it was inevitable that some critics would charge us with "unilateralism." But the charge gets the matter backward. The posture changes will make U.S. alliances capable and useable well into the future. The failure to make such changes could doom our defense partnerships to irrelevance. We want to preserve our alliances, but not in amber.

Though aware that the changes will cause some dislocations, our allies have voiced support, indeed enthusiasm, for the realignment. They know that the measure of U.S. commitment is not a matter of troop levels but of capabilities -- those of our forces in the region and those that can be "surged" in quickly.

A further benefit to this restructuring will be improving the quality of life of military personnel and their families. Accompanied tours abroad are no boon when the service member has to leave his or her family behind to deploy to another location. Right now, for example, the families of European-based soldiers who have been deployed to Iraq or Afghanistan face double separation: from their deployed loved ones and from their extended families back in the United States.

More than three years in the making, the posture realignment reflects the best military advice of U.S. combat commanders and the Joint Chiefs, and input from our allies and partners around the world -- received in extensive high-level consultations -- and from key members of Congress. The standard comment of those briefed on the realignment has been: The United States should have done this a long time ago.

The writer is the undersecretary of defense for policy.