Which amendment is primarily associated with equal protection under the law?

The 14th amendment is primarily associated with equal protection under the law because it includes the Equal Protection Clause. This clause prohibits states from denying any person within their jurisdiction the equal protection of the laws, thereby addressing issues related to discrimination and ensuring that individuals are treated equally by the legal system. The 14th amendment was adopted in 1868 and has since played a crucial role in various civil rights movements, shaping legal standards regarding equality and justice in the United States.

In contrast, the other amendments mentioned do not focus on equal protection. The 10th amendment pertains to the powers not delegated to the federal government being reserved for the states, the 1st amendment secures freedoms related to speech, religion, and assembly, and the 3rd amendment addresses the quartering of soldiers in private homes, none of which are related to the concept of equal protection under the law.