Defenestration

On this day in 1618, the Second Defenestration of Prague took place, igniting the first phase of the Thirty Years War. The hardline Catholic Ferdinand,King of Bohemia and shortly to be Emperor, reversed concessions made to the Protestants by the previous two kings; when the Bohemian Estates objected, Ferdinand dissolved the assembly and sent representatives to the Estates with a letter declaring their leaders' lives and honor forfeit; the leaders responded by throwing the representatives out the window; they fell 70 feet but survived. When Ferdinand was elected Holy Roman Emperor in 1619, the  Bohemian Estates deposed him as king and invited Frederick V, Elector Palatine, to the throne; Ferdinand, with the assistance of Bavaria, invaded Bohemia in 1620 and suppressed the rebellion.

Also, on May 23, 1829, the accordion was patented.