The belief shared by many americans that the united states had a right to own all land to the alantic to the pacific called

Manifest Destiny--belief that God had chosen the American people and they were destined to stretch from sea to sea. 

The term Manifest Destiny rises in popularity following the rise of nationalism in the early 19th century. The concept will encourage expansion into Mexican territory and will cause the annexation of Texas as well as war with Mexico. The Northwest will be gained by treaty with Great Britain. 

In the U.S. it is became of the emancipation proclamation written by Abraham Lincoln that made every citizen of the United States free.