May 25, 240 BC: First recorded perihelion passage of Halley’s Comet.
May 26, 1879: Russia and the United Kingdom sign the Treaty of Gandamak establishing an Afghan state.
May 27, 1703: Tsar Peter the Great founds the city of St. Petersburg.
May 28, 1503: James IV of Scotland and Margaret Tudor are married. A Treaty of Everlasting Peace between Scotland and England signed on that occasion results in a peace that lasts ten years.
May 29, 1886: Chemist John Pemberton places his first advertisement for Coca-Cola, which appears in the Atlanta Journal.
May 30, 1806: Andrew Jackson kills Charles Dickenson in a duel after Dickinson accused Jackson’s wife of bigamy.
May 31, 1859: The clock tower at the Houses of Parliament, which houses Big Ben, starts keeping time.