Ideological Beliefs: The concept of Manifest Destiny, popularized in the mid-19th century, reflected a widely held belief among Americans that it was their destiny to expand across the continent and bring civilization, democracy, and progress to the West. This belief justified territorial acquisition and shaped American attitudes towards westward expansion.
Impact on Slavery: Westward expansion heightened tensions over the issue of slavery. The question of whether newly acquired territories would be slave or free states intensified the sectional divide between the North and the South, ultimately contributing to the outbreak of the Civil War.