The main idea behind the settling of western lands by americans in the early 1800s was known as

the manifest destiny concept.

Explanation:

In the  1800s Americans longed for lands in the American West. they focused on settling at  Ohio River, parts of the Southeast and lands west of the Mississippi River. There were various ways of acquiring the lands which were, purchase from foreign empires, Native American treaties, and war. All these methods were from the concept of Manifest Destiny, which was the idea where people believed that it was inevitable and acceptable for the United States to extend from the Atlantic to the Pacific Oceans.

pretty sure they split up because of religious conflicts.

deseasie in europe