The violence is primarily due to the illegal drug trade. The Coast drug cartel is very active. And drugs generate billions of dollars for the criminal gangs.
The cartels have become powerful, with sophisticated networks of arms, drugs, and money laundering. They control many parts of the country, including the border towns, where they monitor the area with drones and carry out violent attacks.
The Mexican government has been fighting the cartels for years, but the violence in Matamoros seems to be getting worse. The government and local police are often accused of being corrupt and ineffective, with some officials alleged to have links to the cartels.
The U.S. State Department has issued a Level 4: Do Not Travel Advisory for U.S. citizens in Tamaulipas. The alert level is the same as Iran, Iraq, Afghanistan and Syria.
Any U.S. citizen that travels to this part of Mexico should register their travel plans and contact details with the US Department of State so that they can be reached in the event of an emergency.