Not really a single mountain range. The mountains are so old that they have been very heavily eroded down,and it's hard to see them as a single range (if they were - you'd have to refer to geological text-books on the area to find the orogeny).
Going from South to North, and from a motorists' atlas, the principal uplands on the Welsh side of the Welsh / English border are:
Black Mountains, Hergest Ridge, Berwyn, Clywidian Range.
Some countries that have mountains along their borders include the United States (Rocky Mountains along the border with Canada), Chile (Andes Mountains along the border with Argentina), and Nepal (Himalayas along the border with China).
The Alborz Mountains run along Iran's northern border and trace the edge of the Caspian Sea.
zagros mountains
zagros mountains
the Alps mountains and the Apennine mountains.
Rockies
The Alborz Mountains run along Iran's northern border and trace the edge of the Caspian Sea.
The Rio Grande River flows along the border of Mexico and the United States of America. It flows along the border of Texas.
The Great Smoky Mountains are a mountain range rising along the Tennessee-North Carolina border in the southeastern United States.
The two main mountain ranges in France (along the border with Spain and Andorra) and the Alps (along the border with Switzerland and Italy).
The Pontic Mountains run East to West along the Northern border of Turkey.
Those would be the Zagros Mountains, which run along Iran's western border.