Anew york newspaper editor created this term. it was the belief that the land out west rightfully belonged to the united states. (this was later used to justify removing native americans from their land.)

westward expansion

manifest destiny

the great migration

The answer is  "Manifest Destiny."

Explanation:

That doctrine states the right of the Unites States to expand westward and dominate the whole continent as design of divine Providence.  The territorial expansion of the US boundaries was seen as something inevitable.