Even just looking at the US:
Almost all the violence is due to it. Further, it is the excuse for the violation of our 4th amendment rights, also, it is was the excuse for the militarization of the police and the no-knock raids (although terrorism is not part of it).
It's the reason why money laundering is even an issue, and why my banks are on my ass all the time because i work overseas half time. I had a bank shut me down last year because I was travelling to Africa and the balkans and they were just like "we want nothing to do with you"
While DU is split on gun rights, the violence from the drug war is a huge issue. If it wasn't for the violence of the drug war, people wouldn't be as anti-gun, AND there would be less issues because if the violence wasn't there in the first place, there wouldn't be as money gun owners. Then, if it wasn't for the ever-growing police state (mostly due to the drug war) then there wouldn't be as many black helicopter nutjubs stockpiling guns in the first place.
We want to talk about the budget deficit? Think of every single state, local, and federal employee who is involved in the drug war. Think of all the prison guards. The judges, the courthouse employees. think of all the people in prison.. not just the cost of incarcerating them, but also the economic value lost from their not being a part of the economy.
That's just in the US.
In short, perhaps I am a "drug war" loon, but I really believe it is, by far, the number one most important thing to deal with in the world, and I bet that if it all just ended tomorrow that 20 years from now violence around the world would be 20% (at most) of what it is now, and that global economic growth would be a solid 1-2% higher.