All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws. (14th amendment to the Constitution of the United States)
Sen. Jacob Howell said, as he stood up to introduce the 14th amendment:
It prohibits the hanging of a black man for a crime for which the white man is not to be hanged. It protects the black man in his fundamental rights as a citizen with the same shield which it throws over the white man. Ought not the time to be now passed when one measure of justice is to be meted out to a member of one caste while another and a different measure is meted out to the member of another caste, both castes being alike citizens of the United States, both bound to obey the same laws, to sustain the burdens of the same Government, and both equally responsible to justice and to God for the deeds done in the body?
What was the intent as described by one the authors?
Congressman Bingham (Ohio) meant for the 14th to secure “the equal protection of the Constitution of the United States… any of the rights which it guarantees to all men.” (here)
Under this, interracial bans were nixed, with the Alabama Supreme Court stating:
Marriage is a civil contract, and in that character alone is dealt with by the municipal law. The same right to make a contract as is enjoyed by white citizens–means the right to make any contract which a white citizen may make. The law intended to destroy the distinction of race and color, in respect to the rights secured by it.” And again: “One of the rights secured by citizenship, therefore, is, that of suing any other citizen. The civil rights bill now confers this right upon the negro in express terms, as also the right to make and enforce contracts,” “amongst which, is that of marriage with any citizen capable of entering into that relation.”
You can find most of this in any wiki’d synopsis of the 14th.
This trickles down today, as well, when we look at the equal protection clause and applying to men and women under the law, to whites and blacks under the law, and to gays and straights. If they have to same responsibilities, they have the same rights.
Unless you want to amend the 14th (Republicans want to usually amend the 17th), then we do have a history of the equal protection clause applying to “members of different castes,” including cases of marriage. Given that both a State Court and the Federal Court have upheld the idea that marriage is a “civil contract” rather than a religious sacrament, it stands to constitutionally reason as it is governed by municipal laws, it will fall under the 14th.