This viewpoint holds that NATO's post-Cold War enlargement into Central and Eastern Europe was a primary driver of deteriorating relations between Russia and the West, and bears substantial responsibility for the security crises that followed, including the 2014 annexation of Crimea and the 2022 invasion of Ukraine. Holders of this view span a wide range of political traditions — realist international relations scholars, foreign policy restrainers, some European statesmen, and a number of former Western officials — and vary considerably in how much responsibility they assign to Russia versus the West. What unites them is the claim that NATO expansion was strategically reckless and that Western policymakers were warned of the consequences and proceeded regardless.

Advocates of this viewpoint argue that Western leaders made commitments to Soviet and Russian counterparts during the reunification of Germany (1990) that NATO would not expand eastward, and that these commitments were subsequently abandoned. They point in particular to statements made by U.S. Secretary of State James Baker to Mikhail Gorbachev in February 1990, in which Baker reportedly offered assurances that NATO would expand “not one inch eastward.” Declassified documents, they contend, show that similar assurances were given by multiple Western leaders. The Russian government has long cited these assurances as evidence of Western bad faith, and scholars in this tradition argue the historical record supports that reading, even if the assurances were never formalized in a treaty.¹⁾²⁾

The most theoretically developed version of this viewpoint comes from the realist tradition in international relations. Realists argue that great powers have always resisted the expansion of hostile military alliances to their borders, and that Russia's reaction to NATO enlargement was not aberrant behavior but a predictable application of basic security logic. John Mearsheimer, the viewpoint's most prominent academic proponent, argues that the United States would never tolerate a Chinese or Russian military alliance with Mexico or Canada, and that expecting Russia to accept NATO expansion to Ukraine was geopolitically naive. On this account, the relevant question is not whether Putin's actions were morally justified but whether Western policy predictably produced the outcome it claimed to want to prevent.³⁾⁴⁾

Holders of this viewpoint place particular weight on the April 2008 Bucharest Summit, at which NATO declared that Ukraine and Georgia “will become members of NATO.” They argue this declaration — made over the explicit objections of France and Germany, who warned it would provoke Russia — was the inflection point that set the stage for subsequent crises. Russia's invasion of Georgia followed within months. The declaration, they contend, gave Ukraine a target on its back without providing the security guarantee that actual membership would have conferred. William Burns, serving as U.S. Ambassador to Russia at the time, warned in a 2008 cable to Washington that NATO membership for Ukraine was “the brightest of all red lines” for the Russian elite and that proceeding would likely destabilize the country.⁵⁾⁶⁾ Burns later supported robust Western response to the 2022 invasion; holders of this viewpoint cite his 2008 cable as insider corroboration of their structural argument rather than as an endorsement of the full viewpoint.

Some advocates of this viewpoint argue that the West missed genuine opportunities for a cooperative relationship with Russia. They note that Putin raised the possibility of Russian NATO membership directly with Bill Clinton during a June 2000 meeting at the Kremlin, and that the overture was not pursued. Declassified U.S. government documents — notes taken by then-Deputy Secretary of State Strobe Talbott, published by the National Security Archive in August 2025 — record Clinton indicating he was “serious about being ready to discuss NATO membership with Russia.”⁷⁾ Putin also stated publicly in a March 2000 interview with David Frost that he saw no reason Russia could not join NATO. Holders of this viewpoint also point to the 1954 Soviet application to join NATO — rejected by Western powers — as evidence of a longer pattern in which Western institutions were structured to exclude rather than integrate Russia. Whether these overtures were sincere or tactical is disputed even within this viewpoint, but its holders generally argue the West failed to test them adequately.

Holders of this view argue that NATO expansion was not a structural inevitability driven by the preferences of new member states, but a deliberate policy choice made in Washington. They note that figures such as George Kennan — the architect of Cold War containment — publicly warned against expansion in the 1990s, calling it a “tragic mistake” that would inflame Russian nationalism and undermine the prospects for Russian democracy.⁸⁾ Former U.S. Defense Secretary Robert Gates and former National Security Advisor Zbigniew Brzezinski also expressed reservations about the pace or scope of enlargement at various points. Holders of this viewpoint argue this suggests the skeptical position was not marginal but had a presence within mainstream Western policy debate.

This viewpoint has roots in the realist critique of liberal internationalism that emerged in the 1990s. Early skeptics of expansion included Kennan and Senator Sam Nunn, who warned during Senate debate on NATO enlargement in 1997 that the move would foreclose the possibility of a cooperative post-Cold War order. The viewpoint gained wider attention following the 2008 Russia-Georgia war, and moved from the academic margins to mainstream policy debate after Russia's 2014 annexation of Crimea. Mearsheimer's 2014 Foreign Affairs article became one of the most widely read and debated pieces of international relations commentary in recent memory, drawing both fierce criticism and broad engagement.

The Russian invasion of Ukraine in February 2022 produced a sharp divergence within the viewpoint community. Some holders moderated their position or concluded that Russian conduct had exceeded anything NATO policy could justify. Others held that the invasion, while condemnable, vindicated their structural analysis — that expansion had produced precisely the destabilization they had predicted, regardless of the moral status of Russia's response. This fracture is discussed further in the Internal Debates section below.

John Mearsheimer — Professor of political science at the University of Chicago and the viewpoint's most prominent contemporary advocate. Author of The Tragedy of Great Power Politics⁹⁾ and numerous articles applying offensive realist theory to the Ukraine crisis.

George Kennan (1904–2005) — Diplomat and historian, architect of Cold War containment strategy. Warned publicly in 1997 and 1998 that NATO expansion would be a historic error, predicting it would revive Russian nationalism and produce a new adversarial dynamic.

Jack Matlock — U.S. Ambassador to the Soviet Union under Presidents Reagan and George H.W. Bush. Has argued that Western assurances were given to Soviet leaders during German reunification and that subsequent enlargement constituted a breach of good faith.¹⁰⁾

Stephen Walt — Professor of international relations at Harvard Kennedy School. Has consistently argued that NATO expansion reflects liberal hegemonic overreach and that realist restraint would have produced better outcomes.¹¹⁾

William Burns — Career U.S. diplomat who served as Ambassador to Russia from 2005 to 2008 and as CIA Director from 2021 to 2025. His 2008 cable warning against Ukrainian NATO membership represents an insider version of the structural argument, though Burns later supported robust Western response to the 2022 invasion and his position does not map cleanly onto the full viewpoint.

Jeffrey Sachs — Economist and Columbia University professor. Has argued that NATO expansion and Western interference in Ukrainian politics bear substantial responsibility for the 2022 war, situating the argument within a broader critique of U.S. unilateralism after the Cold War.

The sharpest internal division concerns the allocation of responsibility between Western policy and Russian agency. Some holders of this viewpoint — particularly in the realist tradition — maintain a structural framing in which Putin's decisions are treated as rational responses to incentive structures created by Western policy, without requiring moral exculpation of Russia. Others go further and argue that Russian grievances were substantively legitimate and that the West bears primary moral responsibility. A smaller number extend this to qualified sympathy for Russian strategic objectives, which the mainstream of the viewpoint community explicitly rejects.

The full-scale invasion of Ukraine in February 2022 created significant tension within the viewpoint. Those who had argued expansion made war more likely were confronted with the question of whether their analysis implied that Western policy concessions — halting expansion, guaranteeing Ukrainian neutrality — should now be pursued even at the cost of rewarding aggression. Mearsheimer and Walt maintained that a negotiated settlement acknowledging Russian security interests remained the least bad option. Others who had previously shared the structural diagnosis concluded that the invasion's scale and conduct placed it outside the framework of legitimate security responses and shifted their position toward stronger Western support for Ukraine.

There is internal disagreement about how to interpret Russia's early post-Cold War signals, including the Putin-Clinton exchange and the 1954 Soviet application. Some holders of the viewpoint treat these as evidence that integration was genuinely possible and was foreclosed by Western institutional rigidity. Others regard them as primarily tactical — probes designed to test Western resolve or delay enlargement — and base their argument on structural logic rather than claims about Russian intentions.

Even within the viewpoint, there is disagreement about the strength of the 1990 assurances argument. Some, like Mearsheimer, ground their case primarily in realist structural logic and treat the promises question as secondary. Others, like Matlock and Sachs, place the broken assurances at the center of their argument. A minority position holds that the assurances, while real, were oral and contextually limited, and that the more important error was the failure to negotiate a formal treaty establishing European security architecture after the Cold War.

• NATO
• NATO History
• NATO Expansion: Debate
• NATO as Indispensable Alliance
• NATO and U.S. Burden-Sharing
• NATO Obsolescence or Transformation
• European Strategic Autonomy
• Opposition to NATO
• NATO and U.S. Commitment: Debate
• NATO and European Security: Consensus
• War in Ukraine
• Cold War
• Realism (International Relations)

1. Sarotte, M.E. Not One Inch: America, Russia, and the Making of Post-Cold War Stalemate. Yale University Press, 2021.
2. National Security Archive, “NATO Expansion: What Gorbachev Heard,” December 12, 2017. https://nsarchive.gwu.edu/briefing-book/russia-programs/2017-12-12/nato-expansion-what-gorbachev-heard-western-leaders-early
3. Mearsheimer, John J. “Why the Ukraine Crisis Is the West's Fault.” Foreign Affairs, September/October 2014.
4. Mearsheimer, John J. “Playing With Fire in Ukraine.” Foreign Affairs, August 2022.
5. National Security Archive, “Nyet Means Nyet: Russia's NATO Enlargement Redlines,” February 1, 2008. https://nsarchive.gwu.edu/NSAEBB/NSAEBB242/
6. Burns, William J. The Back Channel: A Memoir of American Diplomacy and the Case for Its Renewal. Random House, 2019.
7. National Security Archive, “Putin's Summit Strategy: Newly Declassified Notes from the June 2000 Clinton-Putin Summit,” August 21, 2025. https://nsarchive.gwu.edu/briefing-book/russia-programs/2025-08-21/putins-summit-strategy
8. Friedman, Thomas L. “Foreign Affairs; Now a Word From X.” New York Times, May 2, 1998.
9. Matlock, Jack F. “Who Is the Bully? The U.S. Has Treated Russia Like a Loser Since the Cold War.” Washington Post, March 14, 2014.
10. Mearsheimer, John J. The Tragedy of Great Power Politics. W.W. Norton, 2001.
11. Walt, Stephen M. The Hell of Good Intentions: America's Foreign Policy Elite and the Decline of U.S. Primacy. Farrar, Straus and Giroux, 2018.