I'm not a verified historian on here, but let me give it a shot because I know this answer.

The two most prolific characters that contributed to the disintegration of the Columbian DTO's were US President Ronald Reagan and head of the Medellin Cartel, Pablo Escobar.

Escobar began dealing drugs in the mid 70's, and in less than a decade he had essentially monopolized the cocaine trade from South America into the United States. At his peak it is estimated he was shipping 70-80 tons of cocaine into the US per month and was bringing in about 70 million dollars of income per day as well as having an estimated net worth of 30 billion dollars (that's 80 billion today.)

Reagan was elected president of the United States in 1980. Two years later he literally declared war on illegal drugs and, along with the help of his wife Nancy, began the "Just Say No" campaign. Reagan favored a militant approach to combat the drug trade and in 1986 passed a drug enforcement budget of 1.7 billion dollars. A significant amount of this money was sent straight to Columbia to help the Columbian government train elite task forces to combat the cartels, with the Medellin cartel being the primary target.

Once the amount of money being spent by the United States was at least in the ballpark of the money the cartels had, it was a slow death similar to all large illegal operations.

In 1989, Escobar's men assassinated Luis Carlos Galan, a presidential candidate. This event significantly changed the relationship between Escobar and the Columbian President, Cesar Gaviria. Gaviria's government eventually negotiated a deal with Escobar which saw Escobar cease all operations in exchange for a very luxurious imprisonment in "La Catedral," a prison designed by Escobar for Escobar. This prison was more luxurious than probably 95% of American households at the time (my own words.) It turns out that Escobar in fact did not cease operations while at La Catedral. Upon learning of this, the Columbian president planned to capture Escobar and move him into a traditional prison. Escobar learned of this plot and fled successfully for about a year. The United States assisted the Columbian government in forming the Search Bloc, which used members of the CIA, Delta Force, NAVY SEALS and Columbian assets to hunt down Escobar, which they did on December 2, 1993. During a firefight Escobar and his bodyguard were shot and killed.

The short answer to your question is an extreme amount of American money being spent to combat the Columbian Cartels on their home turf, in addition to the world-class military units and equipment being deployed to South America. The long answer is way more fun if you ask me. As far as reading is concerned, I'm more of a documentary guy, and there are plenty of docs on the Medellin Cartel. King of Coke, youtube link is one of them, but any suggestions on books and documentaries would be appreciated.