Fighting Without Friends

For the United States, preparing for and avoiding great-power war is, in all likelihood, only going to get harder. The country has lost some of its soft power and ability to shape the security agenda in key regions, deficits that will put pressure on its hard power. Strained relationships with allies and partners will create friction for U.S. military operations and defense planners, who will be forced to make difficult trade-offs in the coming years. As they do, they will need to find creative ways of deterring China and Russia through disciplined investments in flexible and innovative capabilities.

The global leadership role that the United States played starting after World War II is no more. Unable to deter or dissuade allies and adversaries, the United States has undermined its ability to set the global security agenda. Its once strong voice in international forums is now more muted, giving space for China and Russia to set the agenda. New security partnerships are already forming without the United States at the center, such as Pakistan and Saudi Arabia’s new defense pact and France and the United Kingdom’s agreement to cooperate on nuclear weapons to deter Russia. Perhaps most worrisome, as U.S. allies hedge their bets by forming new, untested alliances, the United States will have less control over how they exercise or commit to use their nuclear weapons.

Meanwhile, the Trump administration’s indiscriminate and sudden cutoff of U.S. development aid has bred distrust in the Global South and caused hundreds of thousands of deaths, presenting an opening for U.S. rivals to gain the moral high ground. As China takes advantage, countries receiving its economic support may find that it comes with strings attached—namely, agreement with Beijing’s security preferences. As a result, the United States could find that Chinese (and Russian) preferences come to dominate matters as diverse as space security, climate change, biological weapons, information technology, and nuclear nonproliferation.

The absence of trust and support from allies will complicate U.S. military operations. Negotiations with partners have never been seamless, but when it came to freedom of movement for the U.S. military or formal basing relationships, mutually beneficial agreements were workable. In the past, the U.S. military could expect that allies would grant it access to use airspace or bases such as Spain’s in the city of Rota, near Gibraltar, and the joint U.S.-United Kingdom’s in Diego Garcia, in the Indian Ocean. Yet earlier this year, the United Kingdom initially denied the U.S. military access to Diego Garcia for strikes on Iran, and Spain closed its airspace to U.S. fighter jets and refueling aircraft. In Europe, Austrian, French, Greek, Italian, and Swiss officials also imposed constraints on overflights. No longer can U.S. defense planners take access to ports and bases for granted.

Nor can they assume they will retain access to allied intelligence. Earlier in 2026, British and Canadian intelligence officers stopped or placed caveats on intelligence sharing with the United States, citing its illegal targeting of civilians in the Caribbean. For decades, intelligence partnerships such as the Five Eyes—the Anglophone, World War II–era group of the United States, Australia, Canada, New Zealand, and the United Kingdom—have augmented U.S. intelligence. But with the recent erosion of trust, partners can clam up. The result for U.S. officials will be to lose confidence in their own assessments at the same moment that they need more corroborating sources in the age of artificial intelligence and information warfare.

Adding to the difficulty, recent military offenses have depleted critical munitions. In seven weeks of the Iran war, the military likely used more than a quarter of its Tomahawk missiles and half of its Terminal High Altitude Area Defense and Patriot missile defenses. The Pentagon has shifted precious resources from the Korean Peninsula to the Middle East. And when a refueling jet crashed in March, six service members were killed.

Beyond munitions, the United States needs to invest in expensive platforms and emerging technologies simultaneously. Trump has proposed a $1.5 trillion defense budget for fiscal year 2027, which includes billions of dollars for a wide variety of military capabilities. But such high spending is unlikely to be sustainable. If more reconciliation bills add to defense spending as the One Big Beautiful Bill Act of 2025 did, or if the flow of funds is difficult for the military services and industry partners to spend quickly, appropriations could ebb under pressure to cut deficits or prioritize domestic spending.

As the United States decides how much and where to spend on defense, policymakers will have to make difficult trade-offs between investments in emerging capabilities alongside shipbuilding, human capital, munitions, and modernizing major systems such as aircraft carriers and nuclear weapons. The Pentagon will have a clear mandate to buy affordable, autonomous capabilities, given rapid technological advances. Of lower priority might be costly niche capabilities such as hypersonic vehicles that have the potential to strike long-range targets but could lead adversaries to misinterpret their flights as nuclear weapons launches. Russia is firing similar capabilities at Ukraine, but the United States need not respond in kind, just as any exotic or space-based Russian nuclear weapons do not require the United States to develop the same. The U.S. military will have to project power and deter adversaries not by matching or exceeding each adversary’s forces in all domains—air, land, sea, space, and non-kinetic areas such as cyber. Instead, it should compete asymmetrically where it already has advantages.

Future defense policy should build on the United States’ military strengths: its versatile defense platforms and munitions, its professional military personnel, and its world-leading innovation. The U.S. military can deter China and Russia creatively by making careful investments in capabilities that meet one of two criteria: they grant the military flexibility in the most likely theaters of conflict with China and Russia or they hold those countries’ forces at risk asymmetrically, likely through novel technologies. The U.S. military cannot prepare to defeat its main rivals while stretching thin to fight in Greenland, the Americas, or the Middle East.

But defense policy can only go so far. If the United States really wants to make the most of its military in a world of great-power rivalry, it will need to win back the trust it has lost among allies and partners by resuming diplomacy, investing in development, and avoiding overstretch. To show strength, the United States will need to exercise discipline.