International borders are defined lines that separate one country from another. These borders can be marked by natural features like rivers and mountains, or by man-made structures such as fences and walls. They play a crucial role in determining where one nation's laws and regulations apply, affecting everything from trade to immigration. Borders can change over time due to various factors, including treaties, wars, and negotiations. For example, the Treaty of Versailles after World War I resulted in significant border changes in Europe. Understanding international borders is essential for studying global politics, economics, and cultural exchanges between nations.