This is not mere ancient history. It is playing out today, and not just in the consequences of British (or French, or German, or American) imperial misadventures. It informs our Western portrayal of the "East" and our understanding of its peoples. We still see ourselves as the civilized world, the bearers of universal values. And we still portray the "East" as less civilized, more prone to violence, less respectful of human life and liberty.
If imperial has any meaning in the post-colonial 21st century, it certainly means that the (super)power in question has an active interest in attempting to control significant swathes of the planet. In fact, there has never been a power, no matter how "great," that has, in such a militarized way, tried to put its stamp of control on so much of Planet Earth.
Unless teachers "teach outside the textbook," students won't learn about Grenada or about anything else that might call into question the U.S. authority to impose its will whenever it wishes. The specifics of the Grenada invasion are unique, but when students are encouraged to ask critical questions, they can recognize that intervention in Grenada is part of a pattern.