Which of the following reflected an effort to keep slavery out of the entire Mexican Cession?

A. The Wilmot Proviso

B. Popular sovereignty

C. The Missouri Compromise

The correct answer is "A".

The Wilmot Proviso in 1846 was an unsuccessful attempt to ban slavery in the territories acquired from Mexico after the events of the Mexican-American War. It was proposed by Congressman David Wilmot to the House of Representatives. It would eventually pass the House of Representatives but fail to pass the Senate.

The disagreements over this proviso were one of the events that led to the American Civil War.