Once the Treaty of Guadalupe Hidalgo was signed, ending the U.S. War with Mexico (1846–48), politicians in the United States immediately began to squabble over the divvying up of territory. President James K. Polk—a Tennessee slave owner—called on the U.S. General Land Office to draw up a map of the new lands in the West along lines he hoped would be acceptable to all sides of the debate. The map, attributed Ephraim Gilman, detailed all of the U.S. states and territories entirely in terms of square mileage and acreage; no effort was made to discuss the varying populations living in the United States. In Congress, the Whig Party led by Daniel Webster opposed the Treaty of Guadalupe Hidalgo for fear that the addition of so much new territory from Mexico would naturally encourage the spread of slavery. Some southern legislators, on the other hand, such as Jefferson Davis and Sam Houston, opposed the treaty because it did not annex enough of Mexico for their liking; some politicians hoped to expand the United States and its slaveholding territories all the way into South America at some point in the future. Congressman David Wilmot, a member of the anti-slavery Free Soil Party from Pennsylvania, had introduced a proposal to ban slavery in all of the territory acquired from Mexico in the war in the House of Representatives. The proposal failed three times to pass the U.S. Senate, which was dominated by southern advocates of slavery.