I ended up researching the cartels pretty extensively for that 4e piece for Nicaragua. A brief history of the cartels (for those that are interested) looks a bit like this:
Mexico:
In the 80s, there were primarily two large cartels in Mexico, the Gulf Cartel, and the Guadelajara Cartel (The Federation). The Guadelajara Cartel managed most Mexican narco trafficking through the 80s, and were some of the first to establish and maintain relationships with the Colombian cartels. In the late 80s and early 90s, The Guadelajara Cartel was, after facing vastly increased pressure from US and Mexican authorities, intentionally broken up into numerous smaller cartels so as to spread risk of arrest. These cartels included the Juarez, Tijuana, and Sinoloa cartels, amongst many others. This started the Mexican Drug War as the Mexican government began low-intensity conflict against the numerous cartels. The Sinoloa Cartel, headed by "El Chapo", generally was regarded as the most successful of the resultant cartels, and is currently still one of the leading drug traffickers in the region.
Colombia:
Meanwhile in Colombia, you had Pablo Escobar's Medellin Cartel dominating the production of cocaine (and trafficking) throughout the 80s. In the mid to late 80s, the Cali Cartel broke off and started its own affair. After Escobar was killed in the early 90s by the government and Medellin fragmented, the Cali cartel largely took over Colombian drug activity. At the height of the Cali cartel's power (93 to 95), they controlled something like 80% of the world's cocaine market. This ended in 95 when the heads of the Cali Cartel were arrested and put in prison (some allegedly making deals with the Colombian government to get perks and short sentences). Those members of the Cali cartel that refused to stop trading in narcotics went on to form the Norte del Valle Cartel, which controlled most everything in Colombia from 95 until the Twilight War.
Some interesting other tidbits I picked up along the way:
- The Mexican cartels in Central America generally did move their goods over land along the Pacific coast, while the Colombian cartels preferred moving their shipments by boat (or plane when they could) through the Gulf of Mexico.
- The cartels would often pay local "Tumbadores" to steal drug shipments from each other in transit as they passed through Central America. This was frowned upon, but happened all the time, and it was kind of an unspoken understanding between the cartels that they would lose shipments to each other periodically. The Tumbadores were essentially mercs, and although they were in an incredibly dangerous trade, many of them made a living of it.
- The Colombians were known for being more miserly when it came to paying employees and contractors.
- The larger cartels would usually move nice round numbers of product. For example, they might ship 500kg. When the police would report a bust, they'd only list say, 473kg, representing corruption throughout the region when it came to the police (this probably isn't much of a surprise to anyone).
- There's a crazy amount of interconnectivity between the narcotics trade and the world superpowers. You're all aware of the Iran Contra affair and the CIA's involvement no doubt in the 80s, but there was also supposedly heavy involvement by Russian oligarchs and the KGB with the cartels in the 90s, including allegedly Putin himself.
Lastly, as for what would happen to the cartels in the Twilight War? I'd agree that many of them would, while perhaps moving away from the drug trade, still maintain operations and become regional warlords in their areas of operation. With governments collapsing, cartel heads would have the men/weapons/organization to keep their areas under control. I could easily see them rationing out food and medical supplies in return for agricultural and fuel production. Slaves would be found amongst some groups, but not all. Given the outlook of some cartel leaders (especially in Mexico), I could actually see some communities doing rather well for themselves under a cartel's protection in the Twilight War as the cartels move toward insularity and mutual cooperation with the civilians under their purview. I also don't really see them being involved in the invasion of the US, as they'd be more concerned with maintaining their own base of power rather than trying to expand it into such hostile territory.