The cause was attributed to a seemingly never-ending war between the Zeta drug cartel and their rivals. And that may only be a prelude. Miguel Angel Treviño, or "Z-40," has seized the leadership of the cartel from longtime chief Heriberto Lazcano, according to the Associated Press, which describes the new boss as a "brutal assassin" who favors cooking his enemies inside burning oil drums.

For those unnerving reasons, the Zetas have come to define the violence of the drug war, and have lead the U.S. and Mexican governments scrambling to fight them. Arguably Mexico's most powerful drug cartel, the Zetas are now estimated to operate in half of the country, if not more, and have expanded into Guatemala. Aside from unleashing violence, extortion and kidnapping across much of their territory, the Zetas are responsible for the February 2011 death of U.S. Immigration and Customs Enforcement agent Jaime Zapata.

Earlier this month, the Pentagon deployed 200 Marines to Guatemala in a sign the U.S. is getting more direct in going after the Zetas. The Pentagon stresses that the Marines will play a secondary role to the Guatemalans and are limited to merely tracking drug traffickers. But still, that's a lot of Marines now operating in territory shared by the cartel. The U.S. also considers the operation to be only one part of a much larger strategy. Here are five aspects of that war.