Why was it called bloody Sunday?

"Bloody Sunday" refers to several historical events, but most notably, it describes the events of March 7, 1965, in Selma, Alabama, when civil rights activists were violently confronted by law enforcement while marching for voting rights. The brutality of the police response, which was televised, shocked the nation and galvanized support for the Civil Rights Movement. The term is also associated with other events, such as the 1905 Russian Revolution and the 1972 Northern Ireland incident, each marked by violence and significant social upheaval.