Cocaine Smuggling to the US
"The smuggling of cocaine into the United States was dominated by two Colombian drug cartels, the Medellin and Cali cartels, until the early 1990s. Those organizations controlled the entire supply chain. They proved to be the last of their kind, though, as they were dismantled by the mid-1990s. A large number of smaller Colombian cartelitos (small cartels) then emerged and changed the operation of the supply chain by selling cocaine to Mexican groups, as well as to customers in the emerging cocaine markets in Europe. The Mexican groups controlled the trafficking from Mexico into the United States. The shipment methods have changed, too: while originally most of the cocaine shipments went directly from Colombia to the United States by air, nowadays the shipments are mainly sent by boat or semi-submarine to the Central American/Mexican corridor and then overland into the United States."
UN Office on Drugs and Crime, World Drug Report 2012 (United Nations publication, Sales No. E.12.XI.1), p. 84.