QUOTE
Great Britain was duty bound by ... treaty to assist the Portuguese with "troops, archers, slingers, galleys sufficiently armed for war." However, no offer was made by any nation to provide military assistance for the defense of...

Guess what year the Brits failed in their obligation to defend Portugese territory?
Don't answer with political content or your guess and reasons for your guess. Feel free to include humour tho, eg. joke answers to try and throw people off. I will reveal the answer when I've seen a suffecient response.
Oh and I apologise if there was another time that the Brits failed but this one is of particularly political significance ^_^