Westward expansion pushed which issue to the forefront of American
politics in the 1850s?

Westward expansion, particularly west of the Mississippi River, had profound effects on American politics.This expansion created a number of political crises that revolved around the expansion of slavery, dispossession of Native Americans, and federal landholdings in the West.

Explanation:

united states reinforcements contributed greatly to three allied victories in france at: cantigny (first major american battle), argonne (the largest in the united states military history, involving 1.2 million american soldiers), and château-thierry (one of the first actions under general pershing).