The events of Bloody Sunday happened in Selma, Alabama on March 7, 1965 when a civil rights protest march was violently impeded by local law enforcement. John Lewis and Reverend Hosea Williams led the march but were blocked by Sheriff Jim Clark and state troopers at the Edmund Pettus Bridge. Clark and his men repeatedly assaulted the protesters with weapons and tear gas. The horrific images of the day helped progress the voting rights campaign for African-Americans.
Wikipedia
“Bloody Sunday” events
Video
Remembering Selma’s “Bloody Sunday”
John Lewis: The Selma To Montgomery Marches (TIME)
Further Reading
Selma-to-Montgomery March (nps.gov)
From Selma to Montgomery: 5 Things You May Not Know About ‘Bloody Sunday’ (NBC news)
1965 Selma to Montgomery March Fast Facts (CNN)
Lawmakers reflect on Selma beyond Bloody Sunday (CBS news)