From Wikipedia (http://en.wikipedia.org/wiki/War_on_Drugs#Operation_Just_Cause ):
In December 20, 1989, the United States invaded Panama as part of Operation Just Cause, which involved 25,000 American troops. Gen. Manuel Noriega, head of government of Panama, had been giving military assistance to Contra groups in Nicaragua at the request of the U.S. which, in exchange, allowed him to continue his drug trafficking activities, which they had known about since the 1960s. When the Drug Enforcement Administration (DEA) tried to indict Noriega in 1971, the CIA prevented them from doing so. The CIA, which was then directed by future president George H. W. Bush, provided Noriega with hundreds of thousands of dollars per year as payment for his work in Latin America. However, when CIA pilot Eugene Hasenfus was shot down over Nicaragua by the Sandinistas, documents aboard the plane revealed many of the CIA’s activities in Latin America, and the CIA’s connections with Noriega became a public relations “liability” for the U.S. government, which finally allowed the DEA to indict him for drug trafficking, after decades of allowing his drug operations to proceed unchecked. Operation Just Cause, whose purpose was to capture Noriega, killed numerous Panamanian civilians; Noriega found temporary asylum in the Papal Nuncio, and surrendered to U.S. soldiers on on January 3, 1990. He was sentenced by a court in Miami to 45 years in prison.