United States

Expansionism and political crisis at midcentury

Throughout the 19th century, eastern settlers kept spilling over into the Mississippi valley and beyond, pushing the frontier farther westward. The Louisiana Purchase territory offered ample room to pioneers and those who came after. American wanderlust, however, was not confined to that area. Throughout the era Americans in varying numbers moved into regions south, west, and north of the Louisiana Territory. Because Mexico and Great Britain held or claimed most of these lands, dispute inevitably broke out between these governments and the United States.