History of Panama. Two American Presidents (Reagan and H. W. Bush) played a major role in the history of Panama in the late 20th Century. This essay has some details.
From the site:
The United States froze economic and military assistance to Panama in the summer of 1987 in response to the domestic political crisis and an attack on the U.S. Embassy. General Noriega's February 1988 indictment in U.S. courts on drug trafficking charges sharpened tensions. In April 1988, President Reagan invoked the International Emergency Economic Powers Act, freezing Panamanian Government assets in U.S. banks and prohibiting payments by American agencies, firms, and individuals to the Noriega regime. When national elections were held in May 1989, Panamanians voted for the anti-Noriega candidates by a margin of over three-to-one. The Noriega regime promptly annulled the election and embarked on a new round of repression. By the fall of 1989, the regime was barely clinging to power, and the regime's paranoia made daily existence unsafe for American citizens.
On December 20, 1989, President George H.W. Bush ordered the U.S. military into Panama to protect U.S. lives and property, to fulfill U.S. treaty responsibilities to operate and defend the Canal, to assist the Panamanian people in restoring democracy, and to bring Noriega to justice. The U.S. troops involved in Operation Just Cause achieved their primary objectives quickly, and troop withdrawal began on December 27, 1989. Noriega eventually surrendered voluntarily to U.S. authorities. He is now serving a 40-year sentence for drug trafficking.