In 1783, American and British representatives met in Paris to formally end the American Revolutionary War and determine the boundaries of the new republic. The Treaty of Paris granted the United States title to an extraordinarily vast expanse of land. The fledgling nation stretched from the sparsely settled Atlantic Coast in the east, to the Mississippi River in the west; from the Great Lakes in the north, to near the Gulf of Mexico in the south. But the United States was not alone on the continent, as Britain, Spain, France, Mexico, and Russia all claimed or held parts of the territory that lay west of the Mississippi River and south to the Gulf of Mexico.

The U.S. boundaries established in Paris did not stay fixed for long. Over the next seventy years, the United States expanded to the Pacific Ocean and acquired more than two million square miles of contiguous territory through land purchases, treaties, and war.

The dramatic expansion of the United States to the Pacific Coast and into the Southwest in the years 1846-48 is the focus of this lesson. As modern America vies with contentious issues of immigration and ethnic identity, this series of geography and history activities will show students how a brief two years in history had an indelible impact on American politics and culture.