When the United Nations opened for business in 1945, it was a small club. The UN had 51 founding member states in 1945; today it has 193. Most of the newcomers were then colonies, protectorates or mandates, governed from London, Paris, The Hague, Brussels or Lisbon. By the UN's own estimate, almost one third of the world's population in 1945, some 750 million people, lived in territories dependent on colonial powers. Within about thirty years nearly all of those territories had become sovereign states. Few political changes in history have been so large or so fast.

What the word means

Historians use the word decolonization in two senses. The narrow sense is the transfer of sovereignty: a colony becomes an independent state with its own flag, its own government and a seat at the UN. The broad sense includes the slower undoing of colonial control over economies, borders, languages, schools and ideas, a process many people argue is still unfinished. A French journalist used it in 1836 to urge France to leave Algeria, and it spread among scholars in the 1930s, but it became common only after 1945.

It helps to distinguish formal from informal empire. Formal empire means direct rule: foreign governors, foreign laws, foreign armies. Informal empire means influence without formal rule, exercised through debt, trade terms, military bases or friendly local rulers. A country could gain formal independence while remaining under heavy informal influence, a condition critics called flag independence.

Earlier waves

The years after 1945 were not the first great wave of colonial exits. The United States broke from Britain after 1776. Haiti won independence from France in 1804, the only slave revolt in history that founded a lasting state. Most of Spanish and Portuguese America became independent in the 1810s and 1820s. Apart from Haiti, those earlier revolutions were mostly led by settlers or their descendants. The twentieth century wave was different: it was led mostly by colonized peoples themselves, Asians, Africans, Arabs, and Caribbean and Pacific islanders, demanding the right to rule themselves.

Self-determination enters world politics

The idea that drove the wave was self-determination, the claim that a people has the right to choose its own government. During the First World War both Lenin and the American president Woodrow Wilson championed versions of it. In an address to Congress in February 1918, Wilson declared that "'Self-determination' is not a mere phrase. It is an imperative principle of action." Wilson mainly had the peoples of Europe in mind, but his words travelled. The historian Erez Manela has shown that in 1919 nationalists in Egypt, India, China and Korea took Wilson at his word. Manela argues that colonized peoples hoped Wilson's principle applied to them and felt betrayed when it did not. The peace conference left the colonial empires intact, and protests broke out in Cairo, Seoul and Beijing that same year.

The Second World War revived the language. In August 1941 Franklin Roosevelt and Winston Churchill issued the Atlantic Charter. Article 3 of the Atlantic Charter affirmed the right of all peoples to choose their own form of government. Colonial nationalists quickly quoted it. Churchill, however, told Parliament the next month that he meant Article 3 to apply mainly to the nations of Europe under Nazi rule, not to the British Empire. The gap between the principle and the intention became a lever that colonized peoples pulled again and again.

The UN Charter of 1945 went further than the Atlantic Charter, though less far than nationalists wanted. Its Chapter XI dealt with "non-self-governing territories." Under Chapter XI, members that ran such territories accepted a duty to develop self-government there, to promote the well-being of the inhabitants and to report to the UN on conditions. The Charter did not demand independence, but it turned colonial rule into a matter of international concern rather than purely domestic business.

Three roads out

Colonies left empire in three broad ways. Some negotiated a transfer of power through elections and constitutional conferences, as in much of British West Africa. Some fought wars of liberation, as in Indonesia, Vietnam, Algeria and the Portuguese colonies. Some were partitioned as they left, as in India and Palestine. Which road a colony took depended heavily on how many European settlers lived there, how valuable it was to the ruling power and what the great powers wanted.

Worked example: the Philippines in 1946

The Philippines shows how formal and informal empire can coexist. The United States took the islands from Spain in 1898 and then fought a bloody war against Filipino independence fighters. In 1934 Congress passed the Tydings-McDuffie Act, promising independence after a ten-year transition. Japan's invasion in 1941 and 1942 interrupted the plan, but on 4 July 1946 the Republic of the Philippines became independent.

Independence came with strings. The Bell Trade Act of 1946 gave Americans equal rights with Filipinos to exploit the country's natural resources, which required amending the Philippine constitution. The United States also kept major military bases, including Clark Air Base and Subic Bay, under a 1947 agreement. Filipino critics argued that their country had a flag but not full freedom. Defenders replied that the islands needed American aid to rebuild from the war's destruction. The bases stayed until 1991 and 1992, after the Philippine Senate rejected a new treaty. Both sides of the argument illustrate the broad sense of decolonization: sovereignty was transferred in a day, but its meaning took decades to settle.