This chapter traces the evolution of the principle of self-determination, highlighting its deep ties to major historical events in international relations. Originating with the 1648 Treaty of Westphalia, it gained prominence after World War I, particularly through the Versailles Treaty and the League of Nations, which incorporated self-determination into postwar treaties and case law. The principle resurfaced in the 1941 Atlantic Charter and was formally enshrined in the 1945 UN Charter. Subsequent UN resolutions and the 1955 Bandung Conference further reinforced it, especially in the context of decolonization. Considered jus cogens in international law, self-determination is seen as essential for realizing human rights. However, Britain refused to apply this principle in Cyprus, prioritizing strategic interests in the Middle East following its withdrawal from the Suez Canal. Cyprus became Britain’s last stronghold in the region, crucial to Western Cold War strategy and energy security. Britain, backed by the United States and Western Europe, rejected UN appeals for Cypriot self-determination, citing sovereignty and the risk to NATO interests. International institutions, instead of restraining colonial policy, were instrumentalized to uphold it—an issue the next chapter will explore in depth.