Drugs. Guns. Booze. Money. Diamonds. Warm Bodies. What do these things have in common, besides making life more interesting?
Any time a nation closes its boundaries to anything which there is demand for, for reasons just or unjust, immediately and consequentially, a new industry rises up which specializes in getting these goods past the border without atracting the attention of the local gendarmerie. This is simple economics, and simple economics says that if demand is high enough, and supply closed tightly enough, smuggling is a very lucrative business indeed.
What's perhaps more interesting is the fact, historically and in fiction, that the proffesion of smuggler has such an aura of glamor attatched to it. Money, in large enough quantities, is always glamorous. And there's something dashing about the image of the daring blockade-runner landing their boat in the abandoned cove at midnight on the night of the new moon, right under the eyes of the Coast Guard. Of course, modern smuggling is more likely to involve going through airport security with half a lid of heroin shoved up your asshole than anything like that.
Well, to draw a larger picture, the modern smuggling operation can be anything to a few hippies with a van who bring bricks of marijuana over from Mexico when they need the cash, to a European playboy with a few million in a Swiss bank account from moving old Czech AK-47s and land mines to rebels in Central Africa, to large, wealthy, organized, and very, very violent empires built out of dirty money in Colombia or Burma. The common theme here is money. Money, in large enough sums, has an interesting leveling effect on people's morality and personality, bringing the same behaviors to fore-front.
As long as national borders exist, and as long as anything is forbidden, there will be people who move the forbidden things across those borders.