The Stonewall riots were a series of violent conflicts between New York City police officers and groups of gay and transgender people that began during the early morning of June 28, 1969, and lasted several days. Also called the Stonewall Rebellion or simply Stonewall, the clash was a watershed for the worldwide gay rights movement, as gay and transgender people had never before acted together in such large numbers to forcibly resist police.

Taken from http://en.wikipedia.org/wiki/Stonewall_riots