The U.S. withdrawal from the Paris Agreement represented a pivotal setback in global climate governance, disrupting established funding streams, undermining emission reduction targets, and eroding multilateral trust. This systematic review synthesizes empirical and policy analyses to evaluate the political, economic, and scientific consequences of U.S. disengagement, with particular attention to disparities between developed and least developed countries (LDCs). Findings reveal three critical trends: (1) a substantial decline in reliable climate finance, disproportionately affecting LDCs; (2) weakened accountability mechanisms for major emitters; and (3) increased fragmentation in diplomatic negotiations. This paper argues that COP30 in Brazil (2025) must prioritize decentralized leadership models and robust, equitable climate finance mechanisms to restore momentum. Future research should explore quantifiable metrics for translating global stocktake outcomes into actionable national policies for high-emission economies and assess the efficacy of non-state actors in addressing identified governance gaps.