In international relations, the use of power by states remains a fundamental element of foreign policy. This research examines the role and transformation of hard power instruments in foreign policy through systematic literature review methodology. The main objective is to reveal the contextual factors that determine the effectiveness and limitations of hard power instruments. Following PRISMA reporting principles, publications from 1945 to 2025 were examined in Web of Science, Scopus, JSTOR, and Google Scholar databases. From 847 initial studies, 156 core works were selected according to inclusion criteria. The research employed thematic analysis and conceptual mapping methods within a qualitative research framework. The study examined military interventions, economic sanctions, deterrence strategies, hybrid warfare, cyber operations, and energy diplomacy. The findings show that hard power effectiveness depends on five contextual factors: target actor characteristics, implementing state capacity and determination, international environment, implementation form and timing, and integration with soft power elements. Conventional military superiority alone does not ensure success, and weak actors' resistance capacity increased significantly after 1950. Targeted smart sanctions proved 40 percent more effective than comprehensive embargoes. Deterrence strategies function well in traditional interstate relations but remain limited against non-state actors. Major powers prefer hybrid warfare and gray zone tactics at a rate of 76 percent, and cyber space has emerged as a critical new dimension of hard power. The most important conclusion is that using hard power alone produces limited and temporary effects, while its strategic combination with soft power elements generates more legitimate, sustainable, and effective results. Technological developments, the increasing importance of non-state actors, and changes in global power balances demonstrate that hard power is in constant transformation.