What is manifest destiny? why do americans feel they have the right to practice it?

Manifest Destiny is America's destiny to expand - nation of progress. Duty to bring to inferior people civilization!! We are God's chosen nation. If we expand, it will also benefit us economically.

Because its god's nation.

Manifest destiny is the belief that Americans should own land from the Atlantic to the Pacific Ocean. The US went through several hardships to own all of this land, but as Americans, we want our freedom and rights to be as profitable and reach as many people as possible. I think it enables people to realize that we are a free- country with many possibilities and rights that others may or may not have. We are determined. 

I hope this helps!
~kaikers