May 12: Buddha's Birthday in Thailand and Vietnam (2006), International Nurses Day
- 1551 - National University of San Marcos, the oldest university in South America, was founded in Lima, Peru.
- 1881 - Tunisia became a French protectorate.
- 1885 - North-West Rebellion: Louis Riel (pictured) and the Métis rebels were decisively defeated in the Battle of Batoche by Canadian forces under Major-General Frederick Middleton.
- 1926 - A general strike by the trade unions in the United Kingdom ended after nine days.
- 1958 - A formal agreement on the North American Air Defense Command was signed.