International crime syndicates, counter-revolutionary/ fascist sleeper cells, collaborative states, CIA and international intelligence partners, the Catholic Church. All of these work together to make rat lines for the trade of arms, drugs, and laundering. Read operation Gladio for greater detail.

Wall Street: “Yo, there’s some stuff over there that we want to profit from”

Pentagon/CIA: “Okay, fam, we’ll throw some guns at the extremists we just conveniently have in the area. You’ll also get a nice arms manufacturing contract as a bonus”

However if you are asking about logistics, it’s a much messier matter. As in “Islamists in the Arabian peninsula facilitating drug trade in South America via ports in western Europe” level of mess.