I believe the answer is: the Root-Takahira Agreement
In the Root-Takahira Agreement, The united states government agreed to let go of American influence in China and not intervene in Japanese's effort to invade China. In return, the Japanese government had to hand over Philippines' territory to united states.
So according to Google, "Raoul Duke (Johnny Depp) and his attorney Dr. Gonzo (Benicio Del Toro) drive a red convertible across the Mojave desert to Las Vegas with a suitcase full of drugs to cover a motorcycle race. As their consumption of drugs increases at an alarming rate, the stoned duo trash their hotel room and fear l<span>egal repercussions. Duke begins to drive back to L.A., but after an odd run-in with a cop (Gary Busey), he returns to Sin City and continues his wild drug binge."</span>
So we would have rights as Americans .
