The post-World War II international legal order rests upon two fundamental pillars: the prohibition of the use of force under Article 2(4) of the UN Charter and the humanization of conflict through International Humanitarian Law (IHL). Utilizing an analytical-normative methodology and a constructivist theoretical framework, this research analyzes the deconstructive consequences of the twelve-day military aggression by the Israeli regime and the United States in June/July 2025 as a critical juncture in the normative erosion of the current order. The core issue is examining how this twelve-day event transformed from an isolated violation into a systemic catalyst that undermines the intersubjective consensus on foundational rules. This action operated as a "speech act," redefining state identities and interests regarding basic norms. The dual consequences encompass the Jus ad Bellum level—practical invalidation of the non-use of force principle and the paralysis of the collective security system—and the Jus in Bello level, involving systemic breaches of the principles of distinction and proportionality. These breaches included civilian casualties from extensive airstrikes on residential areas, indiscriminate destruction of civilian and nuclear facilities, and targeted assassinations of commanders and scientists, leading to the normalization of total warfare patterns and the weakening of the Geneva Conventions. This process deepens the legitimacy crisis of central institutions like the Security Council and the (ICC), ultimately driving the world toward absolute normative anarchy by destroying minimal normative consensus, potentially signaling the end of the post-war peace project.