So, looking at a global map and making a few assumptions, let's think.

Assuming heroin, or at least the raw materials for making it, is produced in Afghanistan, it needs a market, and a way to get to the market. Transportation can be tricky depending on who's country you are trying to transit, so you also don't want to have to payoff too many people, so the fewer borders you need to cross the better.

So, step one, from Afghanistan into Iran, payoff or control the Iranians to transit country.

Step two, which country to go to next? Turkey would probably be the best option because once in Turkey, you now have access to the Black sea.

Step three, transport "product" to Odesa in Ukraine.

Step four, process and/or distribute "product" into Europe with "war" as cover for distribution.

Step five, possible slaves moving in the opposite direction, but may be a whole different network.

This distribution network has actually been used quite often in history it seems.