A small coup involving a handful of rebels on a small island called Grenada in the Caribbean, which had many U.S. citizen medical students on it, was put down by a small U.S. force during the administration of Ronald Reagan. This had few long term strategic implications or resulted in few lessons learned because it was such a small engagement and was put down so quickly.
The Grenadan military 'engagement' resulting in a whole crop of decorations for the US forces involved, put an end to the regime and the socially progressive political climate in Grenada. By invading a member state of the Commonwealth, the US succeeded for at least once in annoying elements of the UK establishment with its foreign policy. The invasion was condemned by Canada, the UK and the United Nations. Luckily the USA has never illegally invaded anywhere else since then.