The latest shift in Mexico’s perpetually changing criminal landscape is an alliance between the Zetas and the Milenio Cartel, which could be an ominous sign for the Pacific state of Jalisco.

According to Luis Carlos Najera Gutierrez, Jalisco secretary of public security, an alliance between the Zetas and Milenio Cartel (also known as the Valencia Cartel) has been suspected for months, and new evidence confirms the theory. Following a September 11 clash between police and cartel gunmen in Guadalajara that resulted in the death of two suspects and a policeman, Najera claimed that authorities found a message announcing the union of the two groups. Officials have not released the contents of the message, which was allegedly found in a vehicle seized in the aftermath of the shooting.

The violence comes as the latest example of turmoil in Jalisco, a state which has recently seen a tremendous growth in killings linked to organized crime. One of the main generators of violence has been the bitter feud between the Milenio Cartel and their rivals, a group known as the Jalisco Cartel - New Generation (CJNG). As InSight Crime has reported, the two have been at odds for much of the past year, causing the number of executions in the first quarter of 2011 to rise to nearly triple that of the same period last year. In February, the Milenio Cartel posted a series of ominous banners around Guadalajara threatening the CJNG with turning Jalisco into “another Tamaulipas or Guerrero,” two states where violence has recently soared.

The fact that the group has now apparently paired up with the Zetas comes as somewhat of a surprise, and could have a number of implications for the region. Formerly, the Milenio Cartel had been aligned with the Familia Michoacana and the Gulf Cartel in Jalisco under the banner of a coalition known as “La Resistencia,” a group formed with the explicit intention of resisting Zeta incursion into the state. If the Milenio Cartel are now working with the Zetas, it could mean that this alliance has fallen apart.

This suggests that the Zetas have succeeded once again at an activity that has become something of a specialty for them: taking control of areas in turmoil. They have successfully employed this strategy in the past, seizing the opportunity to move into areas where the traditional powers were weakening; including the territory of the Familia in Michoacan, the Gulf Cartel in Monterrey, and the Sinaloa Cartel in Chihuahua.

Meanwhile the Zetas’ former employers and most bitter rivals, the Gulf Cartel, don’t have much of an independent presence in Jalisco outside of the Resistencia. However, evidence suggests that they may be gearing up for a confrontation in the state. On the morning of September 13, 70 armed men arrived in trucks with “CG” ( for Cartel del Golfo, or Gulf Cartel) spray painted on them and briefly took over the town of Juchipila, Zacatecas, located just over the border from Jalisco. The men occupied the town square for several hours and then drove off, in an apparent show of force.

When asked why they had arrived, the men simply replied: “Don’t be worried, don’t be alarmed; we didn’t come here to cause problems or to hurt anyone. We’re only here to do a good cleaning.” Because of the proximity of the town to the state border, the action could have been a signal that the Gulf Cartel is planning to move into Jalisco.

This would make sense. Jalisco is home to a very important coastline for the drug trafficking industry, and would represent a significant asset to the Gulf Cartel. Its capital, Guadalajara, also serves as a key transit point for drug routes running through the middle of the country.

If true, it would explain the shift in the Milenio Cartel’s loyalty: they could be teaming up with the Zetas in order to prevent the Gulf taking over. It would also shed light on the apparent decline of the Resistencia: the Gulf might be pulling out of this coalition in order to establish their own, independent presence in the state.