When James K. Polk was elected president in 1844, the United States was locked in a bitter diplomatic struggle with Britain over the rich lands of the Oregon Territory, which included what is now Washington, Oregon, and Idaho. Texas, not yet part of the Union, was threatened by a more powerful Mexico. And the territories north and west of Texas---what would become California, Nevada, Utah, Arizona, New Mexico, and part of Colorado---belonged to Mexico. When Polk relinquished office four years later, the country had grown by more than a third as all these lands were added. The continental United States as we know it today was established---facing two oceans and positioned to dominate both.
