President Donald Trump is laying waste to the United States’ long-standing system of alliances. By extorting old friends for short-term gain, threatening to annex allied territory, and applying tariffs indiscriminately, he has squandered decades of cooperation that has served U.S. interests worldwide. When Trump eventually leaves office, the next president will have to decide whether to try to restore these ties. If that successor is a Democrat, the instinct may be to revive the alliance framework that existed during the Cold War. But that would be the wrong approach.

The world has changed since Washington built most of its alliances. After World War II, the United States established an alliance system to contain communism in Asia and Europe. When the Soviet threat collapsed, many analysts assumed Washington would scale back its commitments in favor of greater independence. Instead, the United States maintained its obligations and, in Europe, even expanded them. That was easy to do in a world in which the United States had no peer competitor and the risk of having to fight on behalf of an ally was low.

That world is gone. China now poses the first serious challenge to U.S. economic primacy in a century. In East Asia, its military capabilities rival those of the United States. Russia, meanwhile, has emerged from two decades of weakness to invade its neighbors and harass NATO members. And North Korea now has nuclear weapons that can strike the mainland United States.

Washington therefore needs to reassess its alliances and recalibrate them to suit these new realities. It should judge its partners on whether they strengthen U.S. competitiveness with regard to China and on the low likelihood that they could involve the United States in a war that does not serve its interests. Some current U.S. allies pass this test, but not all of them. As future U.S. leaders try to revive cooperation, they must be hard-nosed. An uncritical reembrace of old allies could weaken the United States and even lead to war.

The right allies can make up for the fact that the United States’ relative economic and military power has declined since the 1990s. They can help the United States withstand economic coercion from Beijing by diversifying important supply chains, such as for semiconductors and critical minerals. By building their digital economies around U.S. software and hardware, they can help ensure that Washington, not Beijing, sets technological standards across the globe. Allies can also reduce U.S. defense burdens, either by contributing military capabilities directly or by offering the use of their infrastructure and territory to amplify the reach of U.S. power overseas. Diplomatically, the right allies can back U.S. initiatives in multilateral organizations and complement U.S. efforts to sustain influence across the so-called global South.

But such advantages must be weighed against costs. Treaty alliances are not just diplomatic agreements; they also oblige the United States to go to war, and in today’s world, that commitment is more dangerous than ever. China and Russia are much more confident in their ability to deter or defeat U.S. forces than they were 20 years ago, and hence more inclined to clash with U.S. allies, potentially drawing the United States into a conflict. Alliances also require the Pentagon to prepare for major wars in multiple theaters at once, an expensive pursuit.

When it comes to alliances, more is not always better. A........

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