Addressing Challenges in Horizontal Escalation

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In April 2025, the United States faced a significant challenge when it imposed tariffs on China, leading Beijing to restrict exports of rare earth elements. This move threatened global supply chains allied with the United States and marked the beginning of a broader campaign. Concurrently, as the U.S. and Israel carried out strikes against Iran in February, Tehran expanded its military tactics to involve Gulf states. Additionally, European Union defense ministers recently convened in Brussels to address the growing threat from grey-zone attacks. Even Switzerland, typically reserved in its foreign policy, has raised concerns over Russian activities.

The discovery of a drone loaded with explosives at Germany’s Leipzig Airport in August illustrates a pattern where Beijing, Tehran, and Moscow employ horizontal escalation to challenge U.S. influence. Horizontal escalation involves extending conflicts to new regions or domains, presenting a complex problem for American policymakers. Historically, the U.S. has approached policies in segmented ways, focusing on specific domains like NATO, trade policy, and Taiwan. However, adversaries such as China, Russia, and Iran engage across these domains, challenging the existing U.S. framework.

China, Russia, and Iran, despite having different goals and capabilities, each aim to disrupt the international order established by the U.S. Xi Jinping often discusses changes that haven’t been seen in a century. In 2023, while alongside Russian President Vladimir Putin in Moscow, Xi encouraged collaboration to advance such changes. Their cooperation is evident as Iran provided Russia with critical drone capabilities during its weakest moments in Ukraine. Russia reciprocated with military assistance, reportedly aiding Iran in developing supersonic cruise missiles. China has mitigated U.S. pressure on Russia and Iran by supplying crucial items to Moscow’s defense industry and purchasing sanctioned Iranian oil.

U.S. adversaries further support each other informally. Russia’s conflict requires Western air defense missiles, while Iran engages U.S. forces in the Middle East and China prompts Washington to safeguard capabilities for potential scenarios in the South China Sea. Each effort stretches American resources, presenting vulnerabilities.

While U.S. alliances amplify American strength and reach, they provide adversaries with numerous targets. Opponents, unable or unwilling to confront the U.S. directly, might target weaker allies, undermine infrastructure, or disrupt supply chains. To counter these strategies, the U.S. and its allies should focus on denying adversaries easy opportunities for horizontal escalation. This involves diversifying vulnerable aspects, securing what cannot be diversified, building substantial stocks of military capabilities, and encouraging allies to shoulder more responsibilities.

Resilience shouldn’t be the only strategy, as defending every vulnerability would put U.S. adversaries in an advantageous position. Instead, the U.S. and its allies should develop their own options for horizontal escalation. Russian infrastructure sabotage should lead to consequences, such as weapon transfers to Ukraine, finance restrictions on Russia, or seizing assets breaching sanctions. If adversaries apply pressure, they shouldn’t control where consequences fall. EU Defense Commissioner Andrius Kubilius stated, “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.”

Germany, following the Leipzig incident, announced the deployment of IRIS-T air defense missiles and attack drones to Ukraine. This strategic response philosophy should influence interactions with China and Iran. Economic coercion shouldn’t solely be countered with economic measures, nor should grey-zone attacks be challenged only at their origin. America’s responses should foster uncertainty for adversaries regarding where and how the U.S. and its allies will act.

Horizontal escalation can fortify the connections among U.S. allies. By imposing costs on nations beyond the U.S., adversaries might inadvertently unify Washington’s diverse partners. When China reacted to U.S. tariffs by disrupting European supply chains, the U.S. formed a new partnership with Europe focusing on critical minerals. Similarly, China’s support for Iran and Russia’s aid to North Korea could motivate Gulf states and Asian allies to reassess their ties with Beijing and Moscow. As adversaries aim to broaden conflicts, they might unintentionally strengthen the coalition opposing them.

To combat horizontal escalation effectively, U.S. allies must guard against sabotage and coercion, take on a larger share of deterrence, and collaborate more closely to protect critical technologies and supply chains. Additionally, American leadership and reliability are crucial to ensure that openness remains a source of power for the West, not a vulnerability. As adversaries have mastered horizontal strategies, America and its allies must demonstrate their readiness to adopt similar tactics.

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