Which amendment added states to due process of law?

The correct answer is the 14th Amendment because it specifically addresses the issue of due process of law in relation to the states. Ratified in 1868, the 14th Amendment provides that no state shall deprive any person of life, liberty, or property without due process of law. This was a significant expansion of the protections offered under the Constitution, as prior to this amendment, due process protections were understood to apply only at the federal level. The incorporation of the due process clause into the 14th Amendment meant that individuals are protected from state actions that could infringe upon their rights, thereby extending these fundamental rights that were previously applicable only to the federal government.

The other amendments listed do not relate to due process in the same manner. The 11th Amendment deals with the jurisdiction of federal courts in cases against a state, while the 12th Amendment outlines the procedures for the electoral college in presidential elections. The 15th Amendment focuses on prohibiting the denial of the right to vote based on race, color, or previous condition of servitude. None of these amendments have the direct impact on due process that the 14th Amendment does.