A growing chasm in operational practice is opening up between the United States and its allies in NATO. This rift is putting the Atlantic alliance at risk. Yet no one in Washington seems to be paying attention.

The escalating use of unmanned aerial vehicles to strike terrorist suspects in an increasing number of operational environments from the Arabian Peninsula to Southeast Asia, coupled with the continued use of military commissions and indefinite detention, is driving a wedge between the United States and its allies.

Attitudes across the Atlantic are hardening fast. This isn’t knee-jerk, man-on-the-street anti-Americanism. European governments that have tried to turn a blind eye to U.S. counterterrorism practices over the past decade are now forced to pay attention by their own courts, which will restrict cooperation in the future.

As recently as last month, the German federal prosecutor’s office opened a probe into the October 2010 killing of a German national identified only as “Buenyamin E.” in a U.S. drone strike in Pakistan. There are at least four other similar cases involving German nationals and several reported strikes involving legal residents of the United Kingdom.

In March, Polish prosecutors charged the former head of Polish intelligence, Zbigniew Siemiatkowski, with “unlawfully depriving prisoners of the their liberty” because of the alleged role he played in helping to establish a CIA secret prison in northeastern Poland in 2002–2003.

Last December, British Special Forces ran afoul of the UK courts for informally transferring two Al Qaeda suspects detained in Iraq, Yunus Rahmatullah and Amanatullah Ali, to U.S. forces. The British government has been instructed to recover the men from U.S. custody or face legal sanctions that could result in two senior ministers being sent to prison.

Perhaps the most dramatic example illustrating the gap that has opened up between the United States and its European allies concerns the 2009 in absentia conviction of twenty-three U.S. agents in an Italian court for the role they played in the extraordinary rendition of radical Imam Hassan Mustafa Osama Nasr from Milan to Cairo.

Britain, Poland, Italy and Germany are among America’s closest military partners. Troops from all four countries are currently serving alongside U.S. forces in Afghanistan, but they are now operating within a very different set of constraints than their U.S. counterparts.

The European Court of Human Rights established its jurisdiction over stabilization operations in Iraq, and by implication its writ extends to Afghanistan as well. The British government has lost a series of cases before the court relating to its operations in southern Iraq. This means that concepts such as the right to life, protection from arbitrary punishment, remedy and due process apply in areas under the effective control of European forces. Furthermore, the possibility that intelligence provided by any of America’s European allies could be used to target a terrorism suspect in Somalia or the Philippines for a lethal drone strike now raises serious criminal liability issues for the Europeans.

The United States conducts such operations under the legal theory that it is in an international armed conflict with Al Qaeda and its affiliates that can be pursued anywhere on the globe where armed force may be required. But not one other member of NATO shares this legal analysis, which flies in the face of established international legal norms. The United States may have taken issue with the traditional idea that wars are fought between states and not between states and criminal gangs, but its allies have not.

The heads of Britain’s foreign and domestic intelligence services have been surprisingly open about the “inhibitions” that this growing divergence has caused the transatlantic special relationship, telling Parliament that it has become an obstacle to intelligence sharing. European attitudes are not going to change—the European Court of Human Rights is now deeply embedded in European life, and individual European governments cannot escape its oversight no matter how well disposed they are to assist the United States.

The United States has bet heavily on the efficacy of a new array of counterterrorism powers as the answer to Al Qaeda. In doing so it has evolved a concept of operations that has much more in common with the approach to terrorist threats taken by Israel and Russia than by its European partners. There has been little consideration of the wider strategic cost of these tactics, even as the Obama administration doubles down and extends their use. Meanwhile, some of America’s oldest and closest allies are beginning to place more and more constraints on working with U.S. forces.

NATO cannot conduct military operations under two competing legal regimes for long. Something has to give—and it may just be the Atlantic alliance.

Tom Parker was formerly policy director for Terrorism, Counterterrorism and Human Rights at Amnesty International USA. He is also a former officer in the British Security Service (MI5).