NATO’s Article 5 collective-defense clause has been invoked only once in its history, after the 2001 terrorist attacks, and traders assign just a 5.9% chance of activation before 2027 because recent incidents have triggered only Article 4 consultations. Ongoing Russia-Ukraine fighting has produced isolated airspace violations, including Polish and Estonian drone and jet incursions in 2025, prompting NATO’s Operation Eastern Sentry and enhanced eastern-flank deployments without crossing the armed-attack threshold. The July 2026 Ankara summit saw allies, including the United States, reaffirm commitments and accelerate defense spending, reinforcing deterrence. Historical precedent, the requirement for unanimous consensus on any invocation, and the absence of direct attacks on NATO territory continue to underpin the strong market consensus that formal activation remains unlikely through the end of 2026.