Nation-level competition represents a structural reconfiguration of the global economic order, extending beyond traditional military rivalry to encompass technological supremacy, industrial control, and financial influence. This chapter examines the dynamics of major power competition through the lenses of the U.S.-Japan trade conflicts and the ongoing U.S.-China strategic rivalry, analyzing how nations contend across sectors such as semiconductors, artificial intelligence, and critical supply chains. It introduces the Thucydides Trap as a framework for understanding systemic tensions arising from power transitions. The analysis further highlights how such competitions drive technological decoupling, supply chain realignment, and policy-driven market fragmentation.