Why did the United States invade the island of Grenada? to prevent a Communist government from spreading to other Caribbean islands to use Grenada as base to blockade Cuba to keep out terrorists from the Western Hemisphere

The main reason why the United States invaded the island of Grenada was "to prevent a Communist government from spreading to other Caribbean islands", but it was also to protect the lives of almost 1,000 Americans who were living on the island at the time.