This nonpartisan policy brief, written by an ACE fellow, is republished by The Fulcrum as part of our partnership with the Alliance for Civic Engagement and our NextGen initiative — elevating student voices, strengthening civic education, and helping readers better understand democracy and public policy.

Key Takeaways

• The Treaty on Open Skies, enacted in January 2002, allowed 34 member countries to fly unarmed aircraft over each other’s territory to monitor military activity.
• The United States withdrew in November 2020, citing repeated Russian violations. Russia followed in December 2021, effectively ending the treaty.
• The collapse is part of a broader breakdown of arms control agreements between the U.S. and Russia, leaving fewer formal tools to prevent miscalculation between nuclear powers.

What is the Treaty on Open Skies?

The Treaty on Open Skies was an arms control agreement that allowed member countries to fly unarmed aircraft over each other’s territory to take photographs and gather information about military forces and activities. The idea for Open Skies was first proposed by the U.S. President Dwight Eisenhower in 1955, during the height of the Cold War. Eisenhower believed that if the Soviet Union and the U.S. could observe each other’s military movements openly, both sides would feel less threatened and less likely to misread a situation and escalate tensions into open conflict.

At the time when the Treaty was introduced, Russia (formerly the Soviet Union) rejected the idea of this treaty, but not without reason. At the time, the U.S. had a significant advantage in aerial surveillance technology, which meant an open skies deal would have allowed American aircraft to gather far more useful intelligence over Soviet territory than Soviet aircraft could gather over the U.S.

Without a formal agreement in place, the U.S. continued gathering intelligence through secret means. In May 1960, a CIA U-2 spy plane was shot down over Soviet airspace. The Soviets had been tracking U-2 flights for years but lacked a weapon that could reach the aircraft’s high altitude, until they developed a surface-to-air missile capable of doing so. The shootdown was an embarrassment for the Eisenhower administration, which had publicly denied conducting spy flights. However, the administration was forced to admit the truth when the Soviets came forth with the pilot and the wreckage as evidence.

Despite this controversy, the concept was revived in 1989 by President George H.W. Bush, as Mikhail Gorbachev—the leader of the Soviet Union—was more open to cooperation in the shifting political landscape of the late Cold War. The Treaty was officially signed in Helsinki in March 1992 by the United States, Canada, Russia, and 22 other European nations as original signatories. Over the following decade, additional states ratified the treaty independently, bringing the total membership to thirty-four countries by the time it officially entered into force on January 1, 2002.

How did Treaty Work?

Under the treaty, each member country was assigned a quota of how many flights it could conduct over other countries’ territories each year and how many flights from other countries it had to accept. The U.S. and Russia each had the largest quotas, reflecting the size of their territories. By 2019, members had conducted over 1,500 observation flights in total.

The types of cameras and sensors allowed on the aircraft were regulated and had to be certified. The maximum image resolution permitted was thirty centimeters, which is less detailed than imagery available through commercial satellites. This was intentional, as the goal was transparency and trust-building rather than high-level espionage. Any country wanting to add new technology to its Open Skies aircraft had to have it approved by the Open Skies Consultative Commission, which met monthly at the Organization for Security and Co-operation in Europe (OSCE) headquarters in Vienna.

Why did the Treaty Collapse?

Tensions over the treaty had been building for years before its collapse. The United States accused Russia of repeatedly breaking the rules, including blocking flights of Kaliningrad (a Russian territory on the Baltic Sea), restricting access near the Georgian border, and refusing to allow certain flight paths. Russia denied all accusations and argued that the U.S. was misrepresenting normal operational decisions as violations.

In May 2020, President Donald Trump announced that the United States would withdraw from the treaty, citing Russian noncompliance. The withdrawal took effect in November 2020. European allies, who had benefitted significantly from the treaty and lacked the advanced satellite capabilities of the U.S., urged Washington to stay but the Trump administration declined.

Russia’s response was swift. In January 2021, Russia announced its own intention to withdraw, arguing that because the U.S. was gone, remaining members could no longer guarantee that data gathered from Open Skies flights would not be shared with the U.S. As a result, Russia formally left the treaty in December 2021. With both the United States and Russia gone, the treaty lost most of its strategic value, as the two countries it was most designed to make transparent to each other were no longer participating.

What Does the Collapse Mean for the U.S.?

The end of the Open Skies Treaty did not happen by itself. It followed the U.S. withdrawal from the Intermediate-range Nuclear Forces (INF) Treaty in 2019, and it came at a time when the last remaining major nuclear arms control agreement between the U.S. and Russia, the New START Treaty, was also under strain. Each of these agreements was part of a collection of rules and transparency measures built up over decades to reduce the risk of war between nuclear powers. As the rules have collapsed and continue to collapse, fewer guardrails remain.

For European allies, the loss of Open Skies was particularly detrimental. Many European countries do not have the sophisticated satellites that the U.S. relies on. Open Skies gave them an independent way to monitor Russian military movements, especially along NATO’s eastern border. Without it, they are more dependent on U.S. intelligence sharing, a dependency that itself has recently become politically complicated.

More broadly, the collapse of the treaty represents a breakdown in the idea that transparency itself can be a security tool. The treaty was created on the belief that letting enemies watch each other reduces fear, miscalculation, and the risk of accidental war. That assumption has not disappeared, but the institutional framework around it has.

Debates Surrounding the Treaty’s Collapse

The U.S. and Russian governments each blamed each other for the treaty’s failure, and the debate over who was really at fault remains contested. The U.S. argued that Russia’s flight restrictions made the treaty one-sided, allowing Russia to observe American facilities in Europe while limiting what others could see inside Russia. Critics of the withdrawal argue that violations, while real, were manageable through diplomacy, and that walking away entirely did more damage than staying in an imperfect treaty.

Another debate centers around what, if anything, should replace it. Some analysts argue that satellites and commercial imagery have advanced enough that Open Skies-style flights are no longer necessary. Others push back, noting that satellites cannot replicate the political and symbolic value of mutual observation. The act of allowing another country to fly over your territory and look is itself a confidence-building gesture that imagery alone cannot replace. With U.S.-Russia relations at their lowest point since the Cold War, a new agreement on this scale is considered unlikely in the near term, but the need for transparency mechanisms between nuclear powers has not gone away.

Conclusion

The Treaty on Open Skies was a rare example of enemies agreeing to watch each other openly as a way to reduce fear and build trust. For nearly two decades, it worked. The flights happened, data was shared, and the system functioned as a quiet but meaningful piece of the European security system. Its collapse, driven by mutual accusations of bad faith, a deteriorating U.S.-Russia relationship, and a broader diversion from arms control, removed one more layer of transparency from an already fragile security environment.

FAQ

What exactly is arms control, and why does it matter?

Arms control refers to agreements between countries that set limits on the types, numbers, or use of weapons. The goal is not to eliminate weapons entirely but to make military competition more predictable and less likely to spiral into war. The Open Skies Treaty was one piece of a larger arms control system built up over the decades between the U.S. and Russia. As that system has broken down, there are fewer agreed-upon rules governing how the world’s two largest nuclear powers interact militarily.

What happened to the U-2 Pilot who was shot down?

The pilot, Francis Gary Powers, survived when his aircraft was hit and parachuted to safety where he was immediately captured by Soviet forces. He was put on trial in Moscow, convicted of espionage, and sentenced to ten years in prison. He served less than two years before being exchanged for a captured Soviet spy in 1962, in one of the first ever prisoner swaps between the U.S. and the Soviet Union.

If Open Skies flights had worse image quality than commercial satellites, why did the treaty matter?

The image resolution cap was actually part of the point. The treaty was not designed for spying. The intention behind the treaty was to build trust between signatories. What mattered was not just the pictures but the act of consent: a country allowing another to fly over its territory and look is a deliberate political gesture that satellites cannot replicate. Satellites fly over every country constantly, without permission. Open Skies flights required advance notice, agreed routes, and representatives from both countries on the same aircraft, turning surveillance into a cooperative act. That political dimension is what the treaty’s supporters say can’t be replaced by better satellite technology.

Mutual Surveillance?: The History and Consequences of the Treaty on Open Skies was first published by ACE and republished with permission.

Margaret Wakefield is an ACE fellow.