The Good Friday Agreement is accepted in a referendum in Northern Ireland with roughly 75% voting yes
20 May 1980
In a referendum in Quebec, the population rejects, by 60% of the vote, a government proposal to move towards independence from Canada.
18 May 1565
The Great Siege of Malta begins, in which Ottoman forces attempt and fail to conquer Malta.
16 May 1832
Juan Godoy discovers the rich silver outcrops of Chañarcillo sparking the Chilean silver rush.
15 May 1252
Pope Innocent IV issues the papal bull ad extirpanda, which authorizes, but also limits, the torture of heretics in the Medieval Inquisition.
14 May 1955
Eight Communist bloc countries, including the Soviet Union, sign a mutual defense treaty called the Warsaw Pact.