Until 1821, Spain ruled the area that now includes Arizona, California, Colorado, Nevada, New Mexico, Texas, and Utah. The Mexican war for independence opened the region to American economic penetration. Government explorers, traders, and trappers helped to open the West to white settlement. In the 1820s, thousands of Americans moved into Texas, and during the 1840s, thousands of pioneers headed westward toward Oregon and California, seeking land and inspired by manifest destiny, the idea that America had a special destiny to stretch across the continent. Between 1844 and 1848 the United States expanded its boundaries into Texas, the Southwest, and the Pacific Northwest. It acquired Texas by annexation; Oregon and Washington by negotiation with Britain; and Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Utah, and Wyoming as a result of war with Mexico.