What happened when Lyndon Johnson federalized the National Guard

Soldiers watch civil rights protesters walking during the third Selma March in Alabama, on March 25, 1965. President Lyndon Johnson federalized the Alabama National Guard to prevent violence against the marchers.

President Lyndon B. Johnson federalized the National Guard in 1965, calling on troops to protect civil rights advocates who were marching from Selma, Ala., to Montgomery.

(Image credit: William Lovelace)