
This was easily accomplished because Mexico had long been a major source of heroin and cannabis, and drug traffickers from Mexico had already established an infrastructure that stood ready to serve the Colombia-based traffickers. By the mid-1980s, the organizations from Mexico were well established and reliable transporters of Colombian cocaine. At first, the Mexican gangs were paid in cash for their transportation services, but in the late 1980s, the Mexican transport organizations and the Colombian drug traffickers settled on a payment-in-product arrangement. Transporters from Mexico usually were given 35% to 50% of each cocaine shipment. This arrangement meant that organizations from Mexico became involved in the distribution, as well as the transportation of cocaine, and became formidable traffickers in their own right. Currently, the Sinaloa Cartel and the Gulf Cartel have taken over trafficking cocaine from Colombia to the worldwide markets.

Although Mexican drug cartels, or drug trafficking organizations, have existed for several decades, they have become more powerful since the demise of Colombia's Cali and Medellin cartels in the 1990s. Mexican drug cartels now dominate the wholesale illicit drug market in the United States. Arrests of key cartel leaders, particularly in the Tijuana and Gulf cartels, have led to increasing drug violence as cartels fight for control of the trafficking routes into the United States.

First, agents from Immigration and Customs Enforcement were found to have been paying informants who were actively committing murders in northern Mexico as far back as 2004.

Then, it was discovered that agents from the US Bureau of Alcohol, Tobacco and Firearms had let guns “walk” from American shops into the hands of Mexican gangsters in the infamous Operation Fast and Furious in 2009 and 2010. Officials had hoped to trace the guns to crime kingpins, but many were traced to murder scenes in Mexico, leading to calls for the heads of top officials in Washington.
And most recently a New York Times story this Sunday highlighted how DEA agents launder drug money in order to entrap gangsters.
The scandals have strained the Mexico-US drug-war alliance, opposition politicians south of the border are saying that the US agents are complicit with drug cartels in the violence that has ripped through the country.
In total, there have been more than 50,000 drug related killings in Mexico since 2006.
“Under the leadership of President Felipe Calderon, cooperation between the US and Mexico is at an all-time high,” DEA Administrator Michelle Leonhart said this year in Congressional testimony.
The U.S. Department of Justice estimates that wholesale earnings from illicit drug sales range from $13.6 billion to $48.4 billion annually. Mexican drug traffickers increasingly smuggle money back into Mexico inside cars and trucks returning to Mexico, likely due to the effectiveness of U.S. efforts at monitoring electronic money transfers.
In the decades since the Drug Enforcement Administration was set up under President Richard Nixon in 1973, agents have discovered that nickel and dime street busts don’t hurt the smugglers. To bring down the kingpins, they have to infiltrate their organizations. This means agents are posing as traffickers and hiring confidential informants among the villains. “To make cases against the major players, we have to get into their world,” said a DEA agent who has posed as a trafficker to infiltrate Mexican cartels. “Otherwise you are just busting the small loads that you are lucky to stumble upon.”

Critics say the core problem is that agents are fighting a war that simply can’t be won.
The biggest step in hurting the business operations of Mexican cartels would be simply to legalize their main product: marijuana. Long the world's most popular illegal drug, marijuana accounts for more than half the revenues of Mexican cartels.
Because governments make drugs illegal, the risk associated with transporting them translates to high rewards for those willing to take that risk. The wholesale price of a single kilo of cocaine, for instance, costs $1,200 in Colombia, $2,300 in Panama, $8,300 in Mexico, and between $15,000 and $25,000 in the U.S., depending on how close you are to the Mexican border. At a retail level on the streets of New York, it can run close to $80,000. With markups like that, the business is bound to keep attracting new entrants, no matter what governments do to stop it.
"We must raise the transaction cost, make it too expensive for them to use Mexico as an export platform relative to other countries," he said. "But the demand itself well, that's not going to go away."
Facts
1. In total, there have been more than 50,000 drug related killings in Mexico since 2006.
http://www.globalpost.com/dispatch/news/regions/americas/mexico/111205/how-dirty-the-war-drugs
2. Felipe Calderón, elected in 2006, sent 6,500 federal troops to the state of Michoacan to end drug violence there (Operation Michoacan).
http://www.miller-mccune.com/politics/fighting-drug-war-creates-drug-war-30617/
3. "We must raise the transaction cost, make it too expensive for them to use Mexico as an export platform relative to other countries," he said. "But the demand itself well, that's not going to go away."
http://online.wsj.com/article/SB10001424052748704254604574614230731506644.html