America’s adversaries are attacking sideways

An Iranian missile is displayed under the country’s national flag in a military exhibition commemorating the anniversary of the start of the 1980-88 Iraq-Iran war at Baharestan Square, in Tehran, Monday, Sept. 28, 2026. (AP Photo/Vahid Salemi)

When the U.S. imposed tariffs on China in April 2025, Beijing restricted exports of rare earth elements and magnets, threatening allied supply chains around the world in a campaign that continues to this day.

When the U.S. and Israel launched strikes against Iran in February, Tehran expanded the battlefield to the Gulf states.

Last month, European Union defense ministers gathered in Brussels to grapple with the rising threat of grey-zone attacks. Even the normally taciturn Swiss government is raising the alarm about Russian actions. The August discovery of an explosive-laden drone at Germany’s Leipzig Airport underscores the larger pattern: Beijing, Tehran and Moscow are increasingly using horizontal escalation to challenge U.S. influence.

Horizontal escalation — the expansion of a conflict to new geographic regions or domains of competition — presents a vexing challenge for American policymakers. Washington tends to organize its policies vertically, into separate domains: NATO, trade policy and Taiwan. America’s adversaries are going sideways, operating across these domains rather than solely within them.

China, Russia and Iran differ greatly in their capabilities and objectives, but each seeks to overturn the U.S.-built international order.

Xi Jinping often speaks of “major changes unseen in a century.” In 2023, Xi famously invoked this same idea while standing beside Russian President Vladimir Putin in Moscow, exhorting the Russian leader, “Let’s push it forward together.”

To pursue their aims, America’s opponents sometimes cooperate. Tehran supplied Moscow with key drone capabilities when Russia was at its weakest in Ukraine. Russia, in turn, has provided Iran with sophisticated military assistance. Moscow is reportedly helping Tehran develop supersonic cruise missiles. China has helped blunt U.S. pressure on both Russia and Iran by supplying Moscow with essential dual-use items for its defense industry and by remaining a major buyer of sanctioned Iranian oil.

But U.S. adversaries support each other even without coordinating formally. Russia’s war consumes Western air defense missiles. Iran ties down American aircraft, ships and interceptors in the Middle East. China’s military buildup forces Washington to preserve scarce capabilities for a possible contingency in the South China Sea. Each of these efforts absorbs American resources that cannot be deployed somewhere else.

This exposes a vulnerability of American power. U.S. alliances multiply American strength and expand its reach. But a global system of allies also presents Washington’s adversaries with more targets. An opponent that is unable or unwilling to confront the U.S. directly can threaten a weaker ally, sabotage its infrastructure or disrupt its supply chains.

To meet this challenge, the U.S. and its allies must first deny adversaries easy opportunities for horizontal escalation. Diversify what is vulnerable, harden what cannot be diversified, build deeper stocks of scarce military capabilities and require allies capable of carrying more of the burden to do so.

But resilience should not be the only strategy. The U.S. cannot defend every vulnerability at all times, and trying to do so would hand its adversaries a permanent advantage. Instead, Washington and its allies should develop horizontal escalation options of their own.

Russian acts of sabotage against European infrastructure should trigger costs in domains the Kremlin values — weapons transfers to Ukraine, restrictions on Russian finance, seizures of sanctions-busting assets. An adversary may choose where to apply pressure, but it should not be allowed to choose where the consequences fall.

As EU Defense Commissioner Andrius Kubilius explained, “if we are facing painful hybrid threats or actions, our answer should be painful in a similar way … Not similar means [necessarily], but pain should be at the same level.” In the wake of the Leipzig incident, for example, Germany announced that it had shipped additional IRIS-T air defense missiles and attack drones to Ukraine.

This same logic should shape competition with China and Iran. Economic coercion need not be answered only with economic measures, and gray-zone attacks need not be met only at the site of the attack. America’s responses should create uncertainty in adversaries’ minds about where and how the U.S. and its allies will respond.

Horizontal escalation can also strengthen the bonds that connect U.S. allies. By imposing costs on countries other than the U.S., America’s adversaries may inadvertently provide Washington’s disparate partners with a common cause.

When China retaliated against U.S. tariffs by cutting European supply chains, Washington responded by forging a new critical minerals partnership with Europe. China’s support for Iran and Russia’s assistance to North Korea can likewise push the Gulf states and America’s Asian allies to reassess their relationships with Beijing and Moscow. In trying to expand a conflict horizontally, America’s adversaries may also be expanding the coalition arrayed against them.

Combating horizontal escalation will require Washington’s allies to guard against sabotage and coercion, assume a greater share of the deterrence burden and coordinate more closely to protect critical technologies and supply chains. But it also requires American leadership and dependability to ensure that openness remains a source of power for the West rather than a vulnerability.

America’s adversaries have learned to go sideways. The U.S. and its allies must show a willingness to do the same.

Peter Rough is director of the Center on Europe and Eurasia at Hudson Institute.