Answer: False.
Explanation: The expansion of U.S. settlement into the west actually led to an increase in conflicts over slavery, rather than a decrease. As settlers moved westward, they brought their beliefs and practices with them, including the institution of slavery. This led to tension and conflict between pro-slavery and anti-slavery groups, as they fought over the issue of whether or not slavery should be allowed in the new territories. The expansion of U.S. settlement into the west also led to the expansion of slavery itself, as slave labor was used to support the growing economy. This further exacerbated the conflict over slavery and contributed to the eventual outbreak of the Civil War. Overall, the expansion of U.S. settlement into the west did not lead to a decrease in conflicts over slavery, but rather to an increase in such conflicts.