Equal Protection Under Law is a constitutional principle that mandates individuals in similar circumstances be treated equally by the law. This concept is primarily derived from the Fourteenth Amendment to the U.S. Constitution, which prohibits states from denying any person equal protection of the laws. In the context of the failure of Reconstruction, it highlights how the promise of equality for formerly enslaved individuals was undermined by systemic discrimination and the emergence of Jim Crow laws that enforced racial segregation.