The evolution of the United Nations can be broadly divided into three distinct phases: the Cold War era, the post-Cold War period, and the 21st century. Throughout these phases, the international landscape has shifted from bipolarity to unipolarity and then toward multipolarity. With the continuous increase in its membership, the United Nations has gradually established an extensive operational system comprising principal organs, specialized agencies, and numerous other bodies. This institutional framework actively advances key pillars of the UN’s mission: peace, development, and human rights, as well as humanitarian assistance and international rule of law. Today, the world is undergoing profound changes unseen in a century. The United Nations faces not only multiple challenges to its own authority and effectiveness but also external shocks such as major-power strategic competition, geopolitical conflicts, and risks posed by emerging technologies. Looking ahead, the United Nations must urgently strike a balance among three key relationships: sovereignty versus human rights, state versus non-state actors, and global versus regional governance, thereby driving its systemic transformation and institutional upgrading.