In the years after 1846, the United States Capitol, like the nation itself, would grow and change. In that year Abraham Lincoln won election to the United States House of Representatives, defeating the Methodist evangelist Peter Cartwright. The Mexican War quickly became the major political issue of Lincoln's term in the Congress. In 1846 President James K. Polk's aggressive policies provoked a war with Mexico. Lincoln opposed the conflict, and he hoped his arguments against the war would make his reputation in the Congress. But instead, Lincoln's criticism of the war proved unpopular back in Illinois. Honoring an earlier promise, he declined to seek re-election and stood aside for a fellow Whig. American victory in the Mexican War wrested huge tracts of territory from Mexico, including lands that today make up all or part of the states of California, Arizona, New Mexico, Utah, and Colorado. The acquisition of this territory placed the question of African-American slavery and its future at the center of American political debate. Pro-slavery southerners looked forward to expanding the peculiar institution into the new lands, and feared that its exclusion there would doom slaveholders to eventual economic extinction. Northerners opposed to slavery itself, or much more frequently, to competition from unpaid labor, mobilized themselves to keep slavery out of the new territories. Together they sparked the sectional crisis that led to the Civil War.