To preserve the constitutionality of the Civil Rights Bill, the Republican Congress passed the Fourteenth Amendment in 1866, and it was ratified by the states in July 1868. It declared that all persons born or naturalized in the U.S. are citizens. It based representative apportionment (the number of delegates a state could send to Congress) according to the whole number of persons in each state, thereby eradicating the three-fifths clause that had counted only a fraction of every slave for purposes of apportionment, which had given the white south power disproportionate to its number of voting citizens, and then denied slaves the ability to vote for their own representatives. Representation was to be reduced accordingly if any male 21 or older was denied the vote; but this clause was never applied in practice, and instead Congress passed the Fifteenth Amendment.
With the Fourteenth Amendment, United States citizenship could no longer be denied on account of race. The word "male" was introduced into the Constitution with the section on voting, thus ensuring universal male suffrage for every American citizen, "excluding Indians not taxed," or those Indians who did not pay taxes because they had not assimilated to western society and its concepts of income and private property. The federal government had empowered itself to prosecute any state that would abridge the privileges and immunities of citizens, deny anyone equal protection under the law, or deprive any person of life, liberty, or property without due process of law. This last "due-process clause" had far-reaching effects that were hardly recognized or foreseeable at the time. It subjected both state and federal power to the Bill of Rights, and in the late nineteenth century, the Supreme Court interpreted the term "person" in the due process clause as applicable to corporations, who were then shielded against "unreasonable" regulation by the states, protecting many nineteenth-century monopolies against trust-busting reforms. Almost a century later, the Supreme Court ruled that abortion is constitutional in the 1979 Roe v. Wade decision, a majority opinion based largely on the right to privacy that the Fourteenth Amendment guarantees. The Fourteenth was—and remains—one of the most significant and far-reaching constitutional amendments in United States history.
President Johnson opposed the Fourteenth Amendment partly because his racial prejudices led him to believe that black people did not deserve the rights of citizens, but also because he did not want an extension of federal power. He thought of the Republicans as having engaged in an enormous usurpation of state authority, which was a radically new concept at the time. Prior to the Civil War, the United States was referred to as a plural noun: "These United States," an association of state governments allied for the common good under a federal branch that supervised their interactions but rarely if ever interfered in their laws or social practices. Ever since the American Revolution and its revolt against the English monarchy, a suspicion of centralized authority had prevailed in America. Yet the attempted secession of the states prompted a reevaluation of the balance of power in government, and suddenly the federal authorities were viewed by many as the best—perhaps the last—refuge of the most oppressed and impoverished citizens. These United States became the United States.
Other, less far-reaching provisions of the Fourteenth Amendment repudiated Confederate debt, guaranteed the Union debt, and specified that Congress had the power to pass laws in order to enforce the amendment.