Slavery increased in Southern states as Northern states took steps to end it. Which answer best explains how this division affected westward expansion?

Question

Existing states fought to keep their slaves from moving westward.
Existing Southern states were finally convinced to abolish slavery.
Existing states fought over whether or not slavery should be allowed in the new territories.
Existing states did not want their slaves to join forces with Native Americans from the West.

Answer 1

The answer that best explains how the division between Northern and Southern states over slavery affected westward expansion is:

Existing states fought over whether or not slavery should be allowed in the new territories.

This conflict over the status of slavery in new states and territories became a significant issue during westward expansion, leading to tensions that contributed to events such as the Missouri Compromise and the Kansas-Nebraska Act.