The Mississippi River
The Snake River forms part of Oregon's eastern border
The Mississippi River forms most of Arkansas's eastern border.
The Black Sea forms a small portion of the Eastern border of Europe. The Mediterranean is also part of the Southeastern border.
The Atlantic Ocean forms most of the eastern border of these regions.
The Atlantic Ocean forms the eastern and southern border of New England.
Eastern Border
Georgia's eastern border is the Atlantic Ocean
The Caspian sea forms Azerbaijan's eastern border.
The Mississippi River forms Tennessee's western border.
France, I believe. The geographic landform at this area would be the Apennies.
Germany
Indiana