The Pacific Ocean and the Bearing Strait (just western Alaska)
The Pacific Ocean.
The Pacific Ocean.
The Rio Grande river is part of such border.
The Mississippi River was the western border in 1787.
The Amazon River is on a different continent, and the Pacific Ocean is on the western border of the US! The bodies of water near or in MIDDLE America are the Mississippi River and the Great Lakes!
Alaska?
black sea
black sea
Pacific
Prior to the Louisiana Purchase in 1803, the western border of the US was mostly the Mississippi River.
US-Mexico border. If you mean the body of water that defines a large stretch of such border, it is the Rio Grande River.
That would be the Pacific Ocean.