Trump’s pressure on NATO is reshaping Europe’s Defenses. Will it break the Alliance?

The U.S. president’s pressure on NATO has not led to a major American withdrawal, but the possibility of a significant troop reduction is pushing European allies to prepare for a future in which they carry more responsibility for their own security.

September 17, 2026

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The Human Frontline

CONSTANTA, Romania At Mihail Kogalniceanu Air Base in southeastern Romania, the changing relationship between the United States and NATO can be seen in an unusual contradiction.

American troops have been reduced, yet the United States continues to rely heavily on the base for military operations.

The base, known as MK has hosted U.S. forces since 1999. Located on NATO’s eastern flank and close to Ukraine, it has become an important part of the alliance’s military presence in the region. About half of the roughly 2,000 American troops stationed there left last year as Washington began reshaping its military presence in Europe but U.S. military activity at the base has continued.

When the base was visited in July, nine American KC-135 Stratotankers were stationed there, supporting U.S. military operations during the war with Iran. More than two months later, the aircraft were still there.

The situation reflects the wider uncertainty surrounding President Donald Trump’s approach to NATO. Trump has repeatedly demanded that European allies spend more on defense and take greater responsibility for protecting the continent. His administration has also considered reducing the number of American troops stationed in Europe.

Yet the United States continues to depend on European military bases to project power across Europe and into the Middle East and North Africa. The result is an alliance under pressure, but not one that has broken.

A possible U.S. troop reduction

The biggest uncertainty facing NATO is the Pentagon’s ongoing review of the American military presence in Europe.

Before a NATO ministerial meeting in Brussels in June, U.S. Defense Secretary Pete Hegseth had considered announcing a reduction of around 25,000 American troops in Europe.

Resistance within the administration prevented that announcement. Instead, Washington launched a six-month review of its military posture and the contributions of NATO allies.

The review is examining the military, financial and political commitments of allied governments. A reduction of around 25,000 U.S. troops remains one possible outcome.

The United States currently has more than 81,000 military personnel in Europe, although the number changes as troops rotate through exercises and deployments. A major reduction would represent a significant change for an alliance that has relied on American military power for generations. But even without a formal U.S. withdrawal from NATO, European governments are increasingly preparing for the possibility that Washington could reduce its role.

Europe prepares to carry more of the burden

European countries have sharply increased defense spending in recent years.

The rise has been driven largely by Russia’s full-scale invasion of Ukraine, which has transformed the security environment across Europe. European NATO members and Canada increased their combined defense spending by 20% in 2025 compared with the previous year.

All NATO members except Spain have agreed to reach spending levels equivalent to 5% of GDP on defense and broader security-related investments by 2035.

For European governments, however, the question is no longer simply how much they spend.It is also how independently they can defend themselves. Several NATO members are examining ways to reduce their dependence on American weapons, military technology and defense companies.

That could have consequences for the U.S. defense industry, which has long benefited from European demand for American military equipment. Trump has argued that greater European defense spending should also create more business for American manufacturers.

But uncertainty over the future of the U.S. security commitment is encouraging some European governments to diversify their sources of military equipment.

Washington still needs Europe

Despite the political tensions, the United States continues to rely heavily on European military infrastructure. Spain remains strategically important because of its access to the Atlantic and Mediterranean. The United States has continued investing in major facilities at Morón Air Base and Naval Station Rota.

Washington announced $400 million in construction contracts for work at Morón this year. Britain also remains important to American military operations. The United States is spending more than $4.2 billion on current and planned projects at seven British air bases.

Romania is expanding Mihail Kogalniceanu Air Base through a roughly $2.7 billion project that could eventually make it the largest NATO air base in Europe. The United States has invested more than $100 million in the expansion.

The continued investment highlights the strategic value of European bases to Washington.

Even as the Trump administration challenges the traditional balance within NATO, American military operations remain closely connected to European territory.

Trust is becoming the bigger question

The most difficult issue for NATO may not be whether the United States formally leaves the alliance.

It is whether European governments continue to believe that Washington would stand beside them in a major crisis.

Article 5 , NATO’s collective-defense commitment is the foundation of the alliance. Under it, an attack against one member is treated as an attack against all.

For decades, the credibility of that promise has depended heavily on American military power.

Now, uncertainty surrounding Washington’s future role is influencing European defense planning. Romania and Poland, both on NATO’s eastern flank, have sought to maintain an American military presence on their territory.

At the same time, European governments are increasing their own capabilities and preparing for a security environment in which they may have to do more without the United States.

The debate is unfolding as Russia continues its war against Ukraine and NATO countries face growing concerns about drones, sabotage and other security incidents near the alliance’s borders.

For Europe, the message is increasingly clear: relying on Washington alone may no longer be considered sufficient.

An alliance changing from within

NATO is not breaking apart. But it is changing.

Trump’s demands have accelerated a debate that was already underway in Europe over defense spending, military readiness and strategic independence. European countries are spending more, expanding their defense capabilities and considering alternatives to American military technology.

At the same time, the United States continues to maintain important bases and military infrastructure across Europe because those facilities remain valuable to American global operations. That leaves NATO in an uncertain position. The alliance remains intact, but the assumptions that sustained it for decades are being tested.

The question facing Europe is no longer simply whether America will remain in NATO.

It is how much Europe can — and will — do for its own security if the American role becomes smaller.

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