This great map from the UN Office on Drugs and Crimes helps explain how illicit goods — everything from guns to drugs to pirated DVDs — travel around the world:
The map is taken from a 2010 report, so global smuggling flows may have shifted a bit. Piracy off the Horn of Africa has declined precipitously, for example, after a global effort to crackdown on it. There are also some big omissions, like the West African slave market. But the patterns in the map are still pretty interesting, for two main reasons.
First, you can see here that global illicit trade isn't just poorer countries exporting illicit goods to rich ones. Yes, that's true in some cases: Afghanistan sends heroin to Europe and Colombia sends cocaine to the US. But, in some big cases, wealthier countries are exporting to poorer ones: look at the flow of counterfeit medicine from China and India to, respectively, West and East Africa.
Second, there's are obvious nexuses between different sorts of illegal markets. For instance, the flow of guns from eastern Europe into Central and East Africa fuels instability and violence in a number of regional countries. That instability weakens local governments, helping the smugglers who get illicit goods out of those countries. The wealthier the smugglers get, the more resources they have to corrupt local import/export officials, making it easier to smuggle in weapons. International crime is linked, and self-perpetuating.