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On March 18, 1938, Mexican President Lázaro Cárdenas signed the oil expropriation decree, nationalising the oil industry held by American and British companies. The measure, which triggered a diplomatic crisis, created the state company Pemex and was one of the most significant acts of economic sovereignty in twentieth-century Latin American history. March 18 is celebrated in Mexico as Expropriation Day.

On March 18, 1871, the Paris Commune began — the first experiment in workers' government in modern history — when the city's national guardsmen rebelled against the Versailles government. The Commune, which lasted 72 days, established radical measures such as separation of Church and State and factory self-management. It was crushed in the "Bloody Week" with thousands of deaths.

On March 18, 1965, Soviet cosmonaut Alexei Leonov performed the first spacewalk in history, leaving the Voskhod 2 capsule for 12 minutes in outer space. On returning, his suit had inflated so much that it would not fit through the hatch and he had to release pressure in an emergency, risking his life. Two months later, American Ed White performed the first American spacewalk.