The significance of United States v. Cruikshank (1876) for the Second Amendment was that:
b.) The Supreme Court affirmed that the Second Amendment applied only to actions by the federal government.
This means that the Second Amendment was interpreted as a restriction on the federal government, rather than on state laws or regulations. The case clarified that the Second Amendment did not limit the states in the same way it restricted the federal government concerning the right to bear arms. This decision helped establish the understanding that the Second Amendment primarily concerns federal authority over gun ownership regulations.