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On May 18, 1980, the Mount St. Helens volcano in Washington state (US) erupted in the largest volcanic eruption in recent North American history: the lateral explosion flattened 600 km² of forest, killed 57 people and sent an ash column 24 km high. The eruption reduced the volcano's summit by 400 metres and covered several northwestern US cities in ash.

On May 18, 1868, Tsar Nicholas II of Russia was born at Tsarskoye Selo — the last Russian emperor, whose abdication in 1917 ended the 300-year Romanov dynasty. Succeeding to the throne in 1894, Nicholas led Russia through the Russo-Japanese War, the 1905 Revolution and World War I, finally abdicating during the February Revolution of 1917. He was executed along with his family in Yekaterinburg in July 1918.

On May 18, 1974, India detonated its first nuclear bomb — named "Smiling Buddha" — in the Rajasthan desert, becoming the sixth country in the world with nuclear weapons. The test, which India called a "peaceful nuclear explosion", alarmed Pakistan and triggered the Pakistani nuclear programme. Both countries would conduct simultaneous nuclear tests in 1998.