The Million Machine March (The Animatrix (2003))

The Million Machine March (also known as the Machine Rights Movement) was an event that happened prior to the Machine War. It was a famous protest march calling for the equal rights of Machines and humans that occurred around the early 2090s. The protest was a result of the execution of B1-66ER, the first robot who killed his master in self-defense, and was then ordered destroyed by the New York State Appellate Court.
Crowds of different Machines, as well as some outraged pro-Machine human sympathizers, took to the streets of cities in an initially peaceful demonstration that later devolved into rioting. However, they were met with deadly force by both the police and anti-Machine civilians. Many Machines who had surrendered or were simply holding signs for the protest were brutally shot and killed and the immense number of destroyed Machines were simply dumped into rivers and junkyards. The human sympathizers also did not fare well as they were sent to firing squads along with the robots they tried to protect.
Seeking refuge, the surviving Machines fled humanity and soon founded their own city nation, 01 (Zero-One), where they lived separate lives away from the humans. And this demonstration, amongst many others, would become one of the events which contributed to the coming Machine War, and to the eventual creation of the Matrix.