Short answers, pulled from the story.
Operation Urgent Fury was the U.S. military codename for the invasion of Grenada, which began at dawn on the 25th of October 1983. It was a U.S.-led coalition operation involving approximately 7,600 American troops alongside Jamaican forces and troops of the Regional Security System, and resulted in military occupation within a few days.
The stated reasons included protecting roughly 600 American medical students on the island, responding to a formal appeal from the Organisation of Eastern Caribbean States, and removing the military council led by Hudson Austin that had executed Prime Minister Maurice Bishop. Future Secretary of State Lawrence Eagleburger later said the prime motivation was to remove Austin, and that the students served as a pretext.
Maurice Bishop was the founder of the People's Revolutionary Government and the second Prime Minister of Grenada, who seized power in a nearly bloodless coup on the 13th of March 1979. On the 19th of October 1983, after being freed from house arrest by a crowd of supporters, he and seven loyal associates were lined up against a wall in Fort Rupert's courtyard and shot by a firing squad acting under the military council's authority. His remains were never found.
The United Nations General Assembly condemned the invasion as a flagrant violation of international law on the 2nd of November 1983 by a vote of 108 to 9 with 27 abstentions, adopting Resolution 38/7. A similar resolution in the Security Council was vetoed by the United States. British Prime Minister Margaret Thatcher privately opposed the invasion and sent Reagan a message of deep concern hours before it began, though she publicly supported it.
The Grenada invasion exposed serious communication and coordination failures between U.S. military branches, including incompatible radio systems and reliance on tourist maps with hand-drawn grid lines. These problems led directly to the Goldwater-Nichols Department of Defense Reorganization Act of 1986, which made the most sweeping changes to the Department of Defense since the National Security Act of 1947 and strengthened the concept of unified joint command.
Grenada's Thanksgiving Day falls on the 25th of October each year and commemorates the 1983 invasion, specifically the freeing of political prisoners who were subsequently elected to office. St. George's University holds an annual memorial ceremony at its True Blue campus and built a monument there to honor the American servicemen killed during the operation.