From the site:
The U.S. invasion of Grenada and the toppling of it's Marxist government can be seen as part of a greater regional conflict. This conflict involved the U.S. and it's Central American and Caribbean allies on one side and Fidel Castro's Cuba, the Sandinista government of Nicaragua and various Marxist guerrilla armies on the other. President Reagan and his administration were concerned that the Marxist government of Prime Minister Maurice Bishop was allowing Cuba to gain undue influence in Grenada, specifically by constructing a military-grade airport with Cuban military engineers.
On October 13, 1983, the Grenadian Army, controlled by former Deputy Prime Minister Bernard Coard, seized power in a bloody coup. The severity of the violence, coupled with Coard's hard-line Marxism, caused deep concern among neighboring Caribbean nations, as well as in Washington, D.C. Also, the presence of nearly 1,000 American medical students in Grenada caused added concern.
However, along with concern, came opportunity. With President Reagan's worldwide efforts to confront what he viewed as the threat by the Soviet Union and other Communist countries (such as Cuba), the turmoil in the Caribbean provided a timely excuse to eliminate a Marxist government and give Fidel Castro a black eye.