This is an excellent question, which I will try to address systematically. As for the social conditions which allow the illicit drug trade to flourish, the families involved in this trade usually have few alternatives—especially children. For example, the crackdown on illicit drug trade by U.S. and local authorities too often (and unfortunately) results in the locking up of low-level criminals involved in the trade. When the individuals locked up in prison are mothers or fathers, their children have nowhere else to turn and so end up (ironically) attracted to the drug trade itself. The same result occurs when schools are sub-par; the best economic prospect for children and young adults is the comparatively lucrative drug trade.
The political circumstance that gives rise to the drug trade is corruption. Because the cartels in Central and South America have become so extensive and lucrative, the police officers themselves have proven vulnerable to succumbing to bribery. There are even discouraging accounts of police retaliating against informants. When the law enforcement agencies cannot be trusted, lawlessness results.
Lastly, the economic conditions that allow drugs to flourish are self-perpetuating, because drugs are addictive substances and consumers are willing to pay any price for them. As far as policy is concerned, legal prohibition of drugs actually fuels the demand for them, driving up the price up even more. Also, when substances and grown and transported illegally, production and sales can be accomplished more cheaply because they are unregulated. This means more profit for the drug farmers and dealers. Finally, because illicit drugs are not regulated by the open market, they are prone to unchecked inflation.