Natural border

From the Middle Ages onwards until the 19th century, France sought to expand its borders towards the Alps, the Pyrenees, and the Rhine River.

One such example is the Rio Grande, which defines part of the border between the United States and Mexico, whose movement has led to multiple conflicts.

For one, China's Song Dynasty built an extensive defensive forest in its northern border to thwart the nomadic Khitan people.

[4] In Chapter IV of his 1916 book The New Europe: Essays in Reconstruction, British historian Arnold J. Toynbee criticized the concept of natural borders.

[5] Specifically, Toynbee criticized this concept as providing a justification for launching additional wars so that countries can attain their natural borders.