I don't remember anything about the 14th amendment being declared unconstitutional, although it has been used in ways differently from that in which it was first intended. Actually, when it was passed the primary intention was to protect corporations, which the law regarded as individuals at that time, but it has since been used to ensure equal protection under the law to all citizens (which I find to be a far more worthwhile use of that amendment). Of course, history books will tell you that equal protection under the law was immediately enforced for all citizens, but the existence of Jim Crow laws for almost a century after the Civil War meant that that was not in fact the case.