Ha pointed out some important points, but it's not the whole picture and it doesn't fully explain the all out war that is going on down in Mexico and spilling over into the U.S.
Compared to Mexico, Colombia is a paragon of honesty and the rule of law. Everything in Mexico is bent, and the government has always been the most bent and corrupt of them all. Colombian drug lords were always at war with their government, but the Mexican drug gangs had the government in their pocket.
Smuggling has always been going on across the Mexico - U.S. border, and moving Colombian Cocaine was just another shipment of illegal stuff. But most of that was just getting it through Mexico and into the United States, usually in a "source city" like Houston. There, the Colombians regained control of the product and distributed it through their organizations in cities like Houston, New York and Miami. It was strictly a continuation of the Mexican tradition of smuggling whatever whenever across the joke of a border.
The original HIDTA concept was an answer to dealing with the Colombian organizations in the U.S., and any focus on the Mexican smuggling groups was kind of incidental. Because of all the heat on the Colombians, and because the Mexicans had gotten smart and started taking payment in Cocaine rather than just cash, the Mexicans had room, time and product to change from being drug smugglers to become drug traffickers. They had access to product, they made a heck of a lot more money from selling rather than smuggling, and they soon developed a vastly superior distribution network across the U.S.
Tons of money flooded into the Mexican drug traffickers' pockets and it was like tossing sticks of dynamite into a bonfire. Everything changed and all the old ways of doing things (that nobody ever got too excited over) were thrown out. Rival gangs started shooting wars to control territory and then the central government tried to step in and found out that it did not control the northern border territories.
To illustrate how bad the problem is, imagine the same thing happening in California. The federal government wants a big Los Angeles drug dealer arrested, but can't get it done because the LAPD, LASO, CHP and California Bureau of Narcotics Enforcement all are employed by the drug dealer. The last head of the DEA office in LA was assassinated (by some CHP officers) when he tried to make a move to arrest the guy. The rest of the DEA office fled the state or feigns not knowing the location of the suspect. The editor of the LA Times writes some editorials about how screwed up this all is, and he gets shot to death the next morning on the I-5. The government sends in the 101st Airborne which promptly gets into a huge battle with local police and ex-special forces troops who now work for the drug dealer. That's what Northern Mexico looks like.
And the problem is spreading:
An affidavit by the Bureau of Alcohol, Tobacco, Firearms and Explosives paints the house as a sort of satellite office for Mexico's Gulf Cartel and its partners known as Los Zetas.
Body armor in the master bathroom, a “machine gun” with a silencer on the floor by a bed, money-counting machines, night-vision equipment, hundreds of plastic bags for packaging drugs in resale quantities and machinery for packing the narcotics were found.
Of the 27 high-powered weapons found in the house, some had rounds chambered and were ready to be fired as if positioned for security, while others were disassembled and appeared ready for smuggling back to Mexico.
Also, there was $500,000 worth of cocaine, nearly $100,000 in cash, and a duffle bag stuffed with documents.
Records contend the drugs were shipped through the house on the way to markets. Bulk cash proceeds were then shipped back to Mexican suppliers, as were the military-style weapons they needed back in Mexico.
http://www.chron.com/disp/story.mpl/metropolitan/6844840.html