The United States has reportedly proposed a new security guarantee for Ukraine, modeled after the collective defense principle of NATO's Article 5. Under this plan, a major Russian attack on Ukraine would be treated as a threat to the broader trans-Atlantic region, obligating allied nations to respond, potentially with military force. This would represent the most robust security commitment the United States has offered Ukraine so far. The proposal also includes a stipulation that Ukraine reduce the size of its military as part of the agreement.