This paper examines why the eastward expansion of NATO triggered a Russian military response only in 2008 and beyond, and not in 1999, when the first round of expansion began. existing scholarship correctly identifies NATO expansion as the root cause of this crisis, but fails to elaborate on the timing gap, the central question this paper sets out to answer. This paper argues that this crisis was not inevitable, but required the alignment of multiple factors simultaneously. This paper draws on Kenneth Waltz’s three-level framework to support the argument. According to Waltz’s three-level framework, Russian aggression only became possible when individual, domestic, and international factors converged simultaneously. At the individual level, the transition from Yeltsin’s western-oriented leadership to Putin’s assertive foreign policy produced very different responses in the face of the same provocation. At the domestic level, Russia’s economic and political situation in the 1990s did not allow it to behave assertively, regardless of intention. At the international level, the shift from a unipolar world order to multipolarity provided Russia with the space and confidence to act. This paper concludes that the crisis was not inevitable and that a more accurate multi-level understanding is crucial to prevent such a crisis in the future.

The liberal world was shaken when the Russian army crossed the Ukrainian border on February 24, 2022. The attack violated the sovereignty of Ukraine, but it was not an unprovoked aggression; rather, its roots go back to the first round of NATO’s expansion eastward in 1999. NATO’s expansion in Eastern Europe was justified by the West as part of a containment policy and a means to sustain stability in post-Cold War Europe (NATO, 2023). But Russia perceived it as a direct threat to its sphere of influence (Mearsheimer, 2014). The question then arises: why did Russia not respond to the first round of expansion in 1999, or even the second round in 2004? And why did it suddenly feel the need to respond militarily in 2008 and beyond?

To answer that question, this paper analyzes three factors: first, the role of leadership; second, the domestic conditions of Russia; and third, the changing world order. This paper draws on the three-level framework of Kenneth Waltz, which argues that any conflict can be understood at three levels: the individual, the domestic, and the international (Waltz, 1959).

Existing scholarship correctly identifies the root cause of this crisis as NATO’s expansion, but fails to answer the timing gap question. This article argues that the crisis was not inevitable, but the alignment of three factors: leadership change, domestic stabilization, and a shifting world order from unipolarity to multipolarity made it possible.

Therefore, understanding the timing of this longstanding crisis is as important as understanding its root cause. In order to resolve this crisis, policy failures must be recognized and addressed; otherwise, escalation will continue.

The existing research on NATO-Russia relations is largely divided into two camps: realists and liberals. According to realists like Mearsheimer, this crisis is the result of NATO’s eastward expansion, which created structural provocation and left Russia with no choice but to respond militarily (Mearsheimer, 2014). Mearsheimer’s argument is compelling but fails to address one critical question: if NATO’s expansion caused Russia’s aggressive response, why did Russia not respond to the first round of expansion in 1999 or the second round in 2004, and only did so in 2008 and beyond? This question will be answered systematically at three levels in this article.

Even within Western policy circles, early warnings were ignored. Kennan cautioned in 1997 that NATO’s eastward expansion was a fatal mistake and would inevitably lead to a crisis in Russia-West relations; a warning that proved prophetic yet was dismissed by the Clinton........

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