John C. Fremont (United States) won attacks on land and at sea in and near California. Zachary Taylor defeated large forces in Mexico. Mexico refused to negotiate, so President Polk ordered forces led by Winfield Scott into Mexico City. Treaty of Guadalupe Hidalgo in 1848 ended the war, giving the United States land originally sought by Slidell (New Mexico, Arizona, California, Texas, and Part of Colorado, Utah and Nevada). Border was set at Rio Grande River. Raised questions of slavery in the new territory. Henry David Thoreau and a young Whig, Abraham Lincoln, opposed the war.