The first United States federal law to define citizenship and affirm that all citizens are equally protected by the law. It was mainly intended, in the wake of the American Civil War, to protect the civil rights of persons of African descent born in or brought to the United States.
The Act was passed by Congress in 1865 and vetoed by United States President Andrew Johnson. on April 5,1866 Congress again passed the bill to support the Thirteenth Amendment, and Johnson again vetoed it, but a two-thirds majority in each chamber overrode the veto to allow it to become law without presidential signature. This marked the first time that the U.S. Congress ever overrode a presidential veto for a major piece of legislation.
John Bingham and other congressmen argued that Congress did not yet have sufficient constitutional power to enact this law. Following passage of the Fourteenth Amendment in 1868, Congress ratified the 1866 Act in 1870.