Why did Mexico believe that Santa Anna's forced signing of
the Treaties of Velasco made them invalid?

Santa Anna signed both a public agreement and the secret treaty, but neither was ratified as a treaty by the Mexican government because he had signed the documents under duress while he was a prisoner.

Explanation:

option b, all states follow similar rules and legal process is the right answer.

the 14th amendment in the constitution of america was enacted in july 1868, which include the citizenship, due process, and the equal protection under the law. this amendment was a response to the issues related to former slaves following the american civil war.

the citizenship clause granted citizenship to all persons born or naturalized in the u.s,.   due process of clause asserted that states may not deny any person "life, liberty or property, without due process of law and the equal protection clause declared that a state may not deny to any person within its jurisdiction the equal protection of the laws. the above mentioned excerpt from the constitution of the united states, ensures the citizenship,due process, and equal protection under the law.