The fragile U.S.-Iran ceasefire announced on April 7, 2026, after 40 days of war came at an opportune time for the United States. Several reports indicate it is running out of weapons amid the conflict.

As a scholar focused on U.S. military deployments, these reports are concerning and somewhat surprising.

After all, the United States spends more money on its military – nearly US$1 trillion annually – than the next nine highest-spending countries combined.

How can the U.S. military be depleting its weapons against a largely isolated country that spends less than 1% of what the United States does?

I believe that gauging U.S. weapons stockpiles provides insight into how the U.S. military may be constrained in the future, and what countries such as Russia and China may learn from the Iran conflict.

The US has a missile problem

Operation Epic Fury, as the U.S. calls the military operation in Iran, has employed a large amount of military assets in a short time. Military analysts suggest the U.S. is running low on Tomahawk missiles, surface-to-surface missiles and air-defense interceptor missiles.

After a month of war, the U.S. had used over 850 Tomahawk missiles, the sea- or ground-launched cruise missile that has a 1,500-mile range.

That represents years of stockpile accumulation. The U.S., for instance, budgeted for 57 Tomahawk missiles in 2025 and procured 22 of them. The U.S. has built roughly 9,000 since the 1980s and may have deployed over 30% of its current stockpile since the start of the Iran war.

The U.S. military has used two types of surface-to-surface missiles at rates that are not sustainable if the Iran conflict were to continue at its previous intensity. These missiles have a range of 200 to 250 miles (320 to 400 km) and are used for precision strikes against military targets, such as air defenses or enemy troops.

The air-defense interceptor missiles used for the Patriot system, a ground-based air defense system, and terminal high-altitude area defense system, or THAAD, are used to protect bases, infrastructure and troops.

The U.S. has eight THAAD systems and has sent munitions from a Korean THAAD system to the Middle East for the Iran conflict.

THAAD systems operate by shooting a missile without an explosive payload. Instead, THAAD interceptors rely on kinetic energy, which is derived from its motion, to destroy incoming missiles. The U.S. has used between 50% to 80% of its THAAD stockpile in its war with Iran, according to the Center for Strategic and International Studies.

The rapid consumption of these resources has forced the U.S. to divert missiles from other regions while seeking new funding and contractors to build missiles. But producing and deploying missiles can take 18 to 24 months because certain components need to be manufactured before being assembled into a final product.

The U.S. has alternatives to these systems, such as the shorter-range, low-cost unmanned combat attack system that uses drones. They are known as LUCAS drones and are based on Iran’s Shahed drone design.

These lower-cost alternatives, however, are less effective and increase the danger to ships, service members and civilians.

Broader concerns

The Iran conflict is not the first time the U.S. has been reported to be depleting its weapons stockpiles. In part, that’s due to its role as the world’s largest supplier of arms, accounting for 43% of global arms exports.

The U.S. has supplied Ukraine with substantial military hardware – missile defense systems, missiles, tanks – for its war with Russia. That has led to delays in weapons shipments, including stinger missiles and Paladin howitzers, to Taiwan, where the U.S. has sent arms since the 1950s to deter China from invading it.

After pausing aid, the Trump administration resumed sending weapons to Ukraine in July 2025. And European support for Ukraine comes through the purchase of U.S. military equipment.

Israel’s war in Gaza and Lebanon has put additional pressure on the U.S. weapons stockpile. The U.S. provides $3.8 billion annually in military aid to Israel, in addition to $16.3 billion since the Oct. 7, 2023, Hamas attacks in Israel.

Whether the U.S. is depleting its weapons because it’s consuming its own stockpile or because of its global commitments, or both, it has ripple effects across the globe. A conflict in the Middle East and new demands on the supply chain for increased production mean there will be shortfalls in Europe and Asia, where U.S.-aligned countries rely upon arms exports for their security.

The US and other powers

The U.S., nonetheless, has evolved its approach to preparing for global threats since the end of the Cold War.

In the 1990s, Washington’s strategy was to be prepared to fight wars in two regions simultaneously. The U.S. has scaled back this 1990s strategy to focus on conflict against a single adversary in a single theater.

The Iran war has nonetheless exposed the limits of U.S. military dominance. And rivals such as China and Russia are learning lessons from the Iran conflict at the United States’ expense.

Michael A. Allen received grant research funding from the Department of Defense's Minerva Initiative, the US Army Research Laboratory, and the US Army Research Office from 2017 to 2021.

Soon after the Israeli-U.S. war in Iran began on Feb. 28, 2026, U.S. President Donald Trump called upon NATO allies to help support the effort. The response of European leaders was at first mixed. Some, like the United Kingdom, offering limited or qualified support. Others — chief among them Spain — refused to assist the U.S. at all.

NATO members’ opposition to getting involved with the conflict hardened further after the alliance decided to sit out the subsequent U.S. blockade of the Strait of Hormuz.

The extent of the division between Washington and other members is such that European leaders have quietly begun considering a plan B should Trump make good on his threats to pull out of NATO altogether.

As experts on foreign policy, overseas military bases and security cooperation, we believe that even though historical tensions within NATO are not new, the recent divisions nonetheless pose a major challenge for the long-term viability of the alliance, particularly in an increasingly fragile U.S.-led international order.

The divisions that preceded Iran

Beyond the recent disagreements over Iran, 2026 has also seen the possibility of conflict between NATO members themselves.

In January, long-standing Trump designs over Greenland seemed closer than ever, with the U.S. verbally, at least, suggesting it was prepared to use economic and military coercion to acquire the territory from Denmark, a NATO ally. Despite tensions having since subsided, Denmark has released unprecedented details about how it prepared to defend against military action by its longtime ally.

While the extent of the Trump-originated rifts are new, NATO member nations disagreeing – sometimes vociferously – is not.

In the 1960s and ‘70s, when the U.S. was embroiled in the Vietnam War, members of Congress called on NATO members to contribute more to their own defense. Those were demands that the first Trump administration would later repeat.

In 2003, the U.S. push to invade Iraq also divided NATO. While some members, like the U.K. and Poland, joined the U.S.-led coalition forces in Iraq, others, such as France and Germany, opposed the invasion. Turkey, another NATO member, notably denied the U.S. use of bases in its territory in the lead-up to the campaign.

The increasing tensions led the NATO secretary-general at the time, George Robertson of Britain, to downplay the growing divide and assure the world that NATO members still supported the United States.

NATO countries have even come close to war with each other in the past. Most notably, Turkey and Greece came to blows several times, usually over their still-unresolved territorial conflict over Cyprus in the Mediterranean.

NATO’s evolving mission

Reducing tensions among European nations was always part of the NATO project. With the two world wars driven in large part by French-German rivalry, reducing intra-alliance conflict was central to NATO’s purpose. The first secretary-general of NATO, Lord Lionel Hastings Ismay, famously described NATO as aimed at “keeping the Russians out, the Americans in and the Germans down.”

With the fall of the Soviet Union, one of NATO’s core pillars collapsed.

In the 1990s, the organization’s mission shifted from an anti-Russian defense pact to promoting European regional security. During this period, NATO took part in conflicts in the Balkans from 1992 to 1999. It still maintains a peacekeeping presence there.

In 2001, when launching its war against Afghanistan, the U.S. invoked Article V, NATO’s collective defense clause, for the first and, to date, only time. This led NATO member nations to become militarily active well beyond Europe’s borders, including operations in Pakistan, the coast of Africa, Libya and Iraq.

The 1990s and early 2000s also saw NATO expand to include several former Soviet republics, a move that Russia opposed as hostile to its interests. In fact, post-Cold War NATO expansion into East Europe has long been one of Russian President Vladimir Putin’s chief grievances against U.S. foreign policy in Europe.

The Russian invasions of Crimea in 2014 and Ukraine in 2022 led to a renewed focus on Russia and Europe’s eastern borders, with NATO member nations coordinating on sanctions and military aid in support of Ukraine’s government. The war also led to another round of expansion, with Finland joining the alliance in 2023 and Sweden in 2024.

Trump’s opposition to NATO

While NATO has grown and its mission focus has changed over time, the Trump administration’s call to action against Iran is not an obvious extension of the organization’s evolved focus.

The war is geographically removed from Europe, and Trump has largely been unsuccessful in making the case for why Iran posed an imminent threat to NATO nations. The United States’ motivations and war aims also remain unclear and have been prone to change.

European countries largely agree on issues like preventing Iran from pursuing an unlimited nuclear program. But they have long preferred diplomatic initiatives – like the 2015 nuclear accord deal with Iran brokered during the Obama Administration – to military strikes.

Part of the disconnect now is how the U.S. under Trump views multilateral institutions compared with his predecessors. While past U.S. presidents have viewed NATO as an extension of the United States’ global interests, they also tended to value the alliance as a whole, despite Washington not always getting its preferred outcomes from it. For Trump, it is far more transactional.

Indeed, the Trump administration has framed the lack of support from NATO nations as evidence of the alliance’s decreased utility to the U.S.

Secretary of State Marco Rubio recently echoed that position, questioning the use of the alliance after several NATO members refused to allow the U.S. to use their airspace to conduct military operations in Iran.

During his first term, Trump also openly questioned NATO’s purpose. And he has repeatedly pressured allies to increase their defense spending, suggesting that allies were cheating the U.S. by an overreliance on American military strength.

The specter of unintended consequences

Even before Trump’s threats during his second term, Europe had already decided to change course. After the invasion of Ukraine in 2022 and the increasing fragility of the United States’ involvement in NATO, European countries began increasing military spending; NATO allies have also set targets for further increases in the coming years.

Germany aims to increase its military personnel by 50% in the next 10 years, and it has created its first permanent military deployment abroad – in Lithuania – since World War II. France has likewise announced plans to expand its nuclear arsenal and use it for extended deterrence for the rest of Europe.

Ironically, more spending may increase the chance of tensions between the Trump administration and NATO members.

Over time, the U.S. has reaped some benefits when allies spend less on their own defense. That’s because the U.S. has historically provided security guarantees for countries in exchange for more say over their foreign policies – something scholars refer to as the security–autonomy trade-off.

However, as the U.S. moves further away from a shared vision with European countries and U.S. policy becomes more volatile, American security guarantees may be less reliable in the eyes of many Europeans. Increased European defense budgets will therefore mean NATO members have more opportunities to assert their preferences against those of the U.S.

A changing role for NATO?

The world for the past 80 years has been characterized largely by U.S. political and military dominance. While it is clear that that world is changing, it is less clear what will replace it.

But understanding NATO’s history and its possible paths forward can give us some clues as to what that world will look like. And contrary to Trump’s short-term aims in nudging NATO allies to rebuild their militaries, a more powerful Europe likely means less U.S. influence in the long term, not more.

Michael A. Allen has received funding from the Department of Defense's Minerva Initiative, the US Army Research Laboratory, and the US Army Research Office.

Carla Martinez Machain has received funding from the Department of Defense's Minerva Initiative, the US Army Research Laboratory, and the US Army Research Office.

Michael E. Flynn has received funding from the Department of Defense's Minerva Initiative, the US Army Research Laboratory, and the US Army Research Office.