During the 1830s and 1840s, national debates over slavery intensified. The most important battles now centered on western territories gained through victory in the war with Mexico. Before 1848, government-sponsored expeditions had opened up vast new lands for American pioneers seeking opportunity, and migrants moved west in growing numbers. Then, following the Mexican-American War and the discovery of gold in California, tens of thousands of men rushed to the Pacific coast seeking riches. But the West was already home to a diverse population that included Indians, Mexicans, Mormons, and missionaries. Pioneers converged, and often clashed, with these groups.