As the nation expanded and its population grew, regional tensions, especially over slavery, led to a civil war—the course and aftermath of which transformed American society.
Key Concept 5.1: The United States became more connected with the world, pursued an expansionist foreign policy in the Western Hemisphere, and emerged as the destination for many migrants from other countries.
Key Concept 5.2: Intensified by expansion and deepening regional divisions, debates over slavery and other economic, cultural, and political issues led the nation into civil war.
Key Concept 5.3: The Union victory in the Civil War and the contested reconstruction of the South settled the issues of slavery and secession, but left unresolved many questions about the power of the federal government and citizenship rights.