He could not join the Marine Corps because he did not yet have his Green Card.
Explanation:
Sergeant Rafael Peralta had a special love for the United States as seen from the copies of the Bill of Rights, the constitution, and his boot camp graduation certificate in his room in his family house in Mexico. After he graduated from Morse High School, located in San Diego in 1997, he immediately wanted to enlist in the Marine Corps but he could not do that because he did not yet have his Green Card then.
When he finally obtained that in 2000, he immediately enlisted in the Marine Corps.
