Monroe Doctrine

 

Ever wonder what prevented the Europeans from affecting any territory or place in the United States of America?

That's because of the Monroe Doctrine which was signed and brought forward during the early 1800s by President Monroe of the United States.

In other words, this prevented the European powers from interfering in American affairs and events, especially for colonial purposes.
Because, if you remember, the U.S. was a former colony of the British Empire before the American Revolutionary War during the late 1700s.