HOUSTON — Authorities in Mexico’s southwestern state of Michoacan say gunmen shot down a police helicopter this week in a remote area where narcotics traffickers operate. The pilot and three police officers died in the crash, the worst such incident in Mexico since a military helicopter crash last year that killed 10 people.

The incident Tuesday in Michoacan comes at a time of increasing violence in Mexico from drug cartels fighting each other as well as law enforcement groups.

Homicides on the rise in Mexico

While Mexico’s organized crime groups have always engaged in violence, there was a dramatic rise in murders after President Felipe Calderon assumed office in 2006 and began a war on criminal gangs. By the time Calderon left office in 2012, the murder count had gone well over 20,000 per year.

Under his successor, President Enrique Peña Ñieto, the murder toll began to subside, but still remains well above 18,000 per year.

Recorded homicides in Mexico during the first six months of this year represent a 15 percent rise over the same period last year. According to Mexico’s National Board of Statistics, the murder rate last year was 16.9 per 100,000. By comparison, the national U.S. murder rate is around 4.5 per 100,000.

Balkanization of drug cartels

Crime experts see various reasons for the uptick in violence, including the imprisonment of Sinaloa cartel leader Joaquin “Chapo” Guzman, which has led to fighting to fill the leadership vacuum. But there are other factors as well.

Tristan Reed is an international crime expert who keeps a special watch on Mexico for Stratfor, a global intelligence company headquartered in Austin, Texas. In a VOA interview, he explained how Mexican crime organizations have become more tightly identified with certain regions.

“Fragmentation, what we call the ‘balkanization’ of organized crime in Mexico, is a trend that has been going on for decades now,” Reed said.

Before 1980, the most powerful organized crime group in Mexico was based in the city of Guadalajara, in Jalisco state in central Mexico. But it fragmented into a number of other groups.

Now, Reed said, smaller gangs have emerged in the states that produce most of the drugs being smuggled. In the area known as “Tierra Caliente,” (the hot land), in Michoacan state, these groups operate on their own, but exist under the same geographic umbrella, as do gangs operating in particular regions in other parts of the country.

“There are distinct organizations that may be fighting with each other, that may be allied with groups from different regions. But ultimately the groups within each umbrella are fairly tight-knit in terms of operations, and allegiances and rivalries can emerge overnight because of that.”

In the past these groups were mainly focused on producing heroin and marijuana, but Reed said they now have their own smuggling operations on the border, and have even set up distribution centers in Texas and other states.