16. Haiti and the Dominican Republic

The border between Haiti [left] and the Dominican Republic [right] leaves you with one question, where did all of the trees go? The river drawn boundary separates the countries who have widely varying deforestation laws, leaving Haiti with a near barren landscape and the DR with a much more enticing green oasis.
15. United States and Mexico

U.S. border protection has kept their land on the border of Mexico [right] fairly barren in order to help stop illegal immigration. Regardless, the border between the two countries is one of the most traveled in the world and stretches a little over 3200 km.