Line or Border That Separates Two Countries

This page is the CodyCross answer for the clue below from Architectural Styles, Group 1165, Puzzle 2 (Symmetrical).

Question is: Line or Border That Separates Two Countries

and the answer is: FRONTIER

Word Meaning:

FRONTIER — The part of a country which borders or faces another country or unsettled region.

Definitions from Wiktionary.