Many Americans Justified westward expansion during the 1840's based on
(1) A belief in Manifest Destiny
(2) A need to preserve the natural environment
(3) The authority of Monroe Doctrine
(4) The constitutional principles in the Bill of Rights

(1) A belief in Manifest Destiny

Explanation:

Manifest Destiny, a phrase coined in 1845, is the idea that the United States is destined—by God, its advocates believed—to expand its dominion and spread democracy and capitalism across the entire North American continent. The philosophy drove 19th-century U.S. territorial expansion and was used to justify the forced removal of Native Americans and other groups from their homes.

Source

https://www.history.com/topics/westward-expansion/manifest-destiny

Number 1 is the correct answer

Explanation:

I remember this

#1 im pretty sure its a.

first second and third

explanation: