C. OAU. Organization of African Unity (OAU) had nothing to do with America.
I believe the answer your looking for is D,
The push factors<span> drive migrants out of their countries of origin, </span>pull factors<span> are responsible for dictating where these travelers end up.
</span>Cited evidence: <span>www.globalization101.org/pull-factors/</span><span />
Answer :
The Mexican-American War
Explanation :
The Mexican-American War allowed for the United States to gain and conquer the Southwest. This war also caused sectional conflict in the years leading up to the Civil War.
For a foreign citizen to become become a U.S. citizen.