The U.S. Supreme Court ruled in the Reed v Reed (1971) case that an Idaho law violated the Equal Protection clause of the 14th Amendment because it discriminated against women. Which principle of the U.S. Constitution applies to this situation?

Question

The U.S. Supreme Court ruled in the Reed v Reed (1971) case that an Idaho law violated the Equal Protection clause of the 14th Amendment because it discriminated against women. Which principle of the U.S. Constitution applies to this situation?
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1 point
Separation of power
Federalism
Judicial review
Popular sovereignty