National borders are the invisible lines that separate one country from another. They help define where one nation ends and another begins, often marked by fences, walls, or natural features like rivers and mountains. These borders can change over time due to treaties, wars, or negotiations, reflecting the dynamic nature of international relations. Borders play a crucial role in a country's identity and governance. They determine who can enter or leave a nation, impacting trade, travel, and security. For example, the United States shares its border with Canada and Mexico, which influences cultural exchange and economic activities between these countries.