When the Soviet Union fell, the military was left with millions and millions of guns and weapons. It was just sitting in the stockpiles of old military warehouses. Criminals figured out how they can buy these weapons for cheap and sell them on the black market. This led to a huge increase in arms trafficking after the cold war and the effects are still being felt today.
The arms traffickers did not care who they were selling the firearms too. They sold a bunch to corrupt dictators in Africa, and the also sold it to rebels who were fighting the corrupt dictators. They also sold it to people regardless of their political motivation or agenda. All they cared about was making money.
This link has some good statistics and information on the arms trafficking industry around the world. Be sure to read it if you want a better understanding of this issue.