When he came back from the Corps
Is when he really got serious
Read a lot of books, started acting all mysterious
The VA is what really made him furious
Told him his condition didn't exist, period

from Lupe Fiasco (Ft. Kavinsky) – American Terrorist III Lyrics on Rap Genius

Meaning

He came back from the marine (corps) and got mentally ill.
He was reading a lot of books on his post traumatic stress disorder (PTSD). PTSD is what made him act mysterious, or in other words: mental.

The department of Veterans Affairs made him furious because they told him his illness doesn’t exist. They provided no support.

The department of Veterans Affairs (VA) provides patient care and federal benefits to veterans and their dependants. If they declare you healthy, like they did with the protagonist, they will not give you these benefits. Period.

To help improve the meaning of these lyrics, visit “American Terrorist III” by Lupe Fiasco (Ft. Kavinsky) Lyrics and leave a comment on the lyrics box