Key concepts in international relations for UPSC aspirants should include theories of diplomacy, global governance, security studies, and foreign policy analysis. Understanding major international organizations, treaties, and geopolitical issues is also vital. Candidates must familiarize themselves with current events impacting global relations, particularly India's role on the world stage. Emphasis should be placed on bilateral and multilateral relations involving key stakeholders. Analyzing case studies and significant historical events will deepen insights into the dynamics of international politics, preparing candidates effectively for related examination questions.