The 14th Amendment to the U.S. Constitution is arguably one of the most important provisions in the constitution because, among other things, it has been interpreted to have the effect of incorporating the bill of rights against the states. Before the twentieth century, the first ten amendments were interpreted to apply only against the federal government — not state governments. As such, the fourth amendment’s prohibition on unreasonable searches and seizures and the first amendment’s guarantees of free speech and free exercise of religion were only good against the federal government. Indeed, unless a state law/constitution provided otherwise, a state government could legally commit an unreasonable search and seizure or pass laws abridging speech.
However, beginning in the early twentieth century, the U.S. supreme court began to determine that an operative effect of the due process clause in the fourteenth amendment was that it incorporated the bill of rights as prohibitions on state authority. As such, the states were bound by the first ten amendments to the constitution. Today essentially all of the bill of rights have been incorporated and applied to the states — most recently the second amendment with the U.S. Supreme Court’s decision in McDonald v. Chicago. Although this does raise questions of the balance of power in our traditional federalist system, it has a direct relevance to civil rights litigation inasmuch as federal law interpreting violations of the bill of rights impacts state rulings/law.