In the shadow of the nuclear age, Mordecai M. Kaplan's "The Religion of Ethical Nationhood" (1970) marks a dramatic philosophical evolution from his earlier focus on Jewish survival to an urgent concern for humanity's collective future. Moving beyond his foundational work "Judaism as a Civilization," Kaplan reimagines Judaism through a naturalistic lens that eliminates supernaturalism while preserving Jewish peoplehood as a religious category. Through textual analysis and philosophical critique, this review examines Kaplan's reconstructionist theology and his radical proposal for "ethical nationhood" as an alternative to traditional religious frameworks. Kaplan envisions restructuring world Jewry as an organic, self-governing society, with Israel serving not as a political center but as a spiritual catalyst. Yet significant tensions emerge between nationalistic consciousness and universal conscience, raising crucial questions about whether ethnic-religious movements can transcend inherent xenophobic tendencies to foster genuine humanistic values. While Kaplan's synthesis of nationalism and humanism demonstrates remarkable intellectual development, the practical viability of "ethical nationhood" as a force for world peace remains problematic, requiring further ideological refinement to resolve the fundamental contradictions between particularistic and universalistic commitments.