1983: USA -Britain U.S. invasion of Grenada.

Ronald Reagan apologizes to Margaret Thatcher for not warning her in advance of the U.S. invasion of Grenada.

To: 
Britain
From: 
USA
Year of Apology: 
1983
Footnote: 
http://www.theguardian.com/politics/2014/nov/10/reagan-apologise-angry-thatcher-grenada-white-house-tapes