They wanted to escape from the harsh descrimination of the South and wanted better job opportunities
The Wilmot Proviso was a piece of legislation proposed by David Wilmot (D-FS-R PA) at the close of the Mexican-American War. If passed, the Proviso would have outlawed slavery in territory acquired by the United States as a result of the war, which included most of the Southwest and extended all the way to California.
Wilmot spent two years fighting for his plan. He offered it as a rider on existing bills, introduced it to Congress on its own, and even tried to attach it to the Treaty of Guadalupe Hidalgo. All attempts failed. Nevertheless, the intensity of the debate surrounding the Proviso prompted the first serious discussions of secession.
The answer is d. Philosophy