A geographical feature that creates a natural border between two countries is often a river or a mountain range. Rivers like the Rio Grande serve as borders between North America’s United States and Mexico, while mountain ranges like the Appalachians can separate regions within a country or between nations. These features can influence political boundaries and trade routes while also shaping cultures and communities along their banks or slopes. Natural borders often present challenges for governance, conservation, and economic interactions, significantly impacting bilateral relations between neighboring countries.