They believed it was a divine duty or their "manifest destiny" to spread across the continent of North America
The doctrine of "Manifest Destiny" held that white Americans had been given a divine mandate to colonize all of North America. The notion of "Manifest Destiny" led to a number of actions intended to exterminate or eradicate the indigenous inhabitants. The figurehead most closely identified with Manifest Destiny was US President James K. Polk (1845–1849). Division tensions over slavery were heightened by Manifest Destiny, which ultimately sparked the Civil War.
To learn more about Manifest destiny click here:
https://brainly.com/question/11669373
#SPJ4