Stratfor's been quite good in covering the American drug war emanating in Mexico and radiating outwards, and they've got a great article about the movement of the drug war into Central America. Essentially, way back in the day, Colombian cocaine would go directly to the US, through points in South Florida, but that was eroded by stepped up enforcement in the area. After that, Mexico became a popular transshipment point, as drugs would fly/swim directly from Colombia to Mexico, from which they would be smuggled across or under America's southern border, and into the largest drug market in the Americas.
However, the perpetual whack-a-mole game continues. Mexico and Colombia have cracked down on the direct shipments, so now Colombia cocaine is taking a more circuitous route to Mexico, overland (or by short-haul air or coast-hugging boats) through the countries of Central America into Mexico. As Stratfor notes, the region has luckily avoided the violence normally associated with the drug trade, and the analysts at Stratfor claim that essentially the reason is that those governments have not been fighting the drug smugglers, and so there's been little violence. This is in line with the constant refrain from anti-drug prohibitionists that it's prohibition and enforcement that causes the violence, not the trade itself.
First, most governments in Central America have yet to launch large-scale counternarcotics campaigns. The seizures and arrests that have been reported so far have generally been the result of regular police work, as opposed to broad changes in policies or a significant commitment of resources to address the problem. More significantly, though, the quantities of drugs seized probably amount to just a drop in the bucket compared to the quantity of drugs that moves through the region on a regular basis. Because seizures have remained low, Mexican drug traffickers have yet to launch any significant reprisal attacks against government officials in any country outside Guatemala. In that country, even the president has received death threats and had his office bugged, allegedly by drug traffickers.
Sadly, the US is not content to leave Central America out of this increasingly bloody war:
For one thing, the Merida Initiative, a U.S. anti-drug aid program that will put some $300 million into Mexico and about $100 million into Central America over the next year, could be perceived as a meaningful threat to drug-trafficking operations. If Central American governments choose to step up counternarcotics operations, either at the request of the United States or in order to qualify for more Merida money, they risk disrupting existing smuggling operations to the extent that cartels begin to retaliate.
It's also relevant to remember that this recent surge in drug-related violence in Mexico and along the border is directly related to crackdowns by the Mexican government in recent years, largely at the behest of the Americans.