The country that forms most of the northern border of the United States is Canada. The country directly to the south is Mexico.
MONGOLIA makes up most of China's northern border.
Rio Grande forms the Southern border of the United states.
Canada
Canada
Canada
Kentucky forms most of the northern border of Tennessee.
ALBORZ
The Black Sea form most of the northern borders of Turkey.
Himalayas
Elburz Mountains
The largest country in the world: Canada