4. United States and Mexico Running from Imperial Beach, California, and Tijuana, Baja California, in the west to Matamoros, Tamaulipas, and Brownsville, Texas, in the east, the 1,950 miles long border separates the United States from Mexico.
The Mexico drug war is the major reason for the border being threatening. A report published by Human Rights Watch criticizes Mexican security forces and estimates more than 60,000 people were killed in drug-related violence from 2006 to 2012.