Answer:
Congress had to decide if new states would be 'free states' or 'slave states
Step-by-step explanation:
Slavery was a significant issue regarding U.S. westward expansion because it raised questions about whether new states formed in the western territories would permit slavery or not. This issue eventually led to political debates and compromises, such as the Missouri Compromise and the Kansas-Nebraska Act, as the United States expanded westward into new territories and states. These debates played a crucial role in shaping the country's future and contributing to the tensions that eventually led to the American Civil War.