The State Department considers five states in Mexico as dangerous for U.S. travelers as war-torn nations like Syria, Yemen and Afghanistan.

Agency officials announced a new numbered classification system for world travel on Wednesday, replacing a confusing array of "travel alerts" and "travel warnings" found on its website. The information is officially for U.S. government employee travel guidance but also serves as a globetrotter's crash course of ongoing risks around the world.

The new classifications range from Level 1 ("Exercise normal precautions") for countries like Canada and Argentina, to Level 4 ("Do not travel"), the highest restriction reserved for active war zones such as Syria and authoritarian countries like North Korea.

But dire travel warnings are notable for Mexico, the U.S.'s neighbor and consistently top foreign destination for American travelers, as the country struggles to blunt rising violence linked to drug cartels and corrupt institutions. The country registered a historic number of homicide investigations in 2017, with 23,101 cases opened in the first 11 months. That is the most since the country began measuring homicide probes in 1997, nearly a decade before the drug war kicked off in earnest in Dec. 2006.

The Level 4 restrictions on five of Mexico's 31 states can be seen as a road map of drug cartel operations.

Continuous gangland clashes fuel violence in Northern Mexico'sTamaulipas as rival cartels seek valuable smuggling routes into South Texas. Sinaloa, the western Mexico headquarters for the cartel of the same name previously led by drug lord Joaquín "El Chapo" Guzmán, is joined by Colima and Guerrero (home to the heroin highway) states further south, where drug cultivation and production churn out illicit drugs.

The mountainous state of Michoacan was so ravaged by cartel violence and absent authorities that citizens created their own police force, known as autodefensas, a movement that spread to other unstable states like Guerrero and are often accused of perpetrating the same violence as the criminals they sought to defend against.

A spike in violence since a decline in 2014 has frayed plans for some of the most sought-after travel destinations that Americans used to heavily frequent. Acapulco, in Guerrero, is the murder capital of Mexico after a decrease in visitors seeking its expansive beaches and resort hotels, and the State Department specifically forbids travel there. But overall, Mexico earns a Level 2 classification - "Exercise increased caution," though the State Department advisory says "violent crime, such as homicide, kidnapping, carjacking, and robbery, is widespread."

Cancun and Mexico City, top destinations for U.S. visitors, are far from restricted territory.

Michelle Bernier-Toth, head of the Office of Overseas Citizens Services, reiterated these travel warnings are not new, but explained changes were made because few people understood the distinctions in the previous, broad rankings, The Washington Post's Carol Morello reported.

"I personally was tired of explaining the difference between a travel warning and a travel alert, even to some of my colleagues," she said. "We needed to make it more accessible to people, to make sure the information was more easily understood using plain language."