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. Eastern migrants, along with immigrants from Germany and Scandinavia, 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. Eager pioneers converged, and often clashed, with these groups.