1848 Map of Western Territories

/tiles/non-collection/p/polk_map_a.xml Image courtesy of the National Archives and Records Administration
On December 5, 1848, President Polk delivered his annual message to Congress, and used this map to illustrate his desired plan for the land acquired through the Treaty of Guadalupe Hidalgo that ended the Mexican-American War. For a sum of $15 million, Mexico ceded territory that included present-day Arizona and New Mexico and parts of Utah, Nevada, and Colorado and renounced any claims to Texas. As these new territories joined the Union, discussion in Congress about the future of slavery intensified. In his speech, Polk stated, “I have heretofore expressed the opinion that that line of compromise should be extended on the parallel of 36° 30' from the western boundary of Texas, where it now terminates, to the Pacific Ocean. . . . If this be done, it is confidently believed a large majority of the people of every section of the country, however widely their abstract opinions on the subject of slavery may differ, would cheerfully and patriotically acquiesce in it, and peace and harmony would again fill our borders.”

The map shows the latitude of 36° 30', the line established by the Missouri Compromise of 1820, north of which slavery was prohibited in the Louisiana territory. Its key lists the square mileage of territory that fell north of it, as well as the total square mileage of free states and slave states. The map represents an important record of Congress’s steps toward the rise of the concept of “popular sovereignty” (the notion that each state had the right to determine its status as free or slave) and the Compromise of 1850, which briefly lessened sectional conflict before the country dissolved into civil war.

The annual message given by presidents, now known as the State of the Union address, is delivered on the Floor of the House of Representatives, so the record copy of the message becomes an official record of the House.