Final answer:
Hernández's lawyers appealed to the United States Supreme Court, marking a historic 'first' as it was the first time the court recognized the 14th Amendment's protections for all ethnic groups.
Step-by-step explanation:
The milestone case was Hernandez v. Texas, and the Supreme Court's decision marked a historic 'first' in that it extended constitutional rights to a group that had been subject to discrimination.
Hernández's lawyers appealed next to the United States Supreme Court, which was a significant legal procedure as it was the first time that the high court recognized that the protections of the 14th Amendment extend to all ethnic groups in the United States.
This recognition was groundbreaking because it confirmed that Mexican-Americans and all other ethnicities have equality under the law, ensuring the broad applicability of the 14th Amendment's equal protection clause.