Final answer:
Andrew Jackson did not veto a civil rights act; instead, it was President Andrew Johnson who vetoed the Civil Rights Act of 1866 due to his white supremacist beliefs, but Congress overrode his veto, making a historical precedent.
Step-by-step explanation:
The question regarding why Andrew Jackson vetoed the civil rights act involves a misconception. It was actually President Andrew Johnson, not Andrew Jackson, who vetoed the Civil Rights Act of 1866. The Act was designed to end the discriminatory Black Codes and grant citizenship and equal rights to all people born in the United States, regardless of race. Despite Johnson's veto, based on his racist beliefs that African Americans did not deserve citizenship, Congress overrode his decision. This marked the first time in history that Congress overrode a Presidential veto on such a substantive piece of legislation, reflecting the changing attitudes towards civil rights during Reconstruction.