 Let's start with the basics. Even under the best-case scenario, controlling the border isn't easy. At nearly 2,000 miles, the border between the U.S. and Mexico is one of the longest in the world. It's the biggest intersection of a wealthy country and a poor country anywhere on the planet. And it's also the world's busiest border, with around a million people and $1.5 billion worth of goods crossing every day.