|Quite typically of me, I didn't think of the obvious image for this page until Peter Rozovsky pointed it out.|
Yes, it's got those old Latin roots, no surprise. The Online Etymology Dictionary tells us that the Latin perfidia goes back to the phrase per fidem dicipere, which means "to deceive through trustingness". The Middle French was perfidie and it hit English in the 1590s. Perfidious Albion (la perfide Albion), as in, "Hey, looking at YOU, England!" came over from France a bit later in the form of a poem of 1793 by a Frenchman named Augustin, although it seems the sentiment predated the poem by, well, centuries.
Wikipedia tells us that there is a particular meaning to perfidy in war, which is actually a war crime. So you can't hold up a flag of surrender and then not surrender. You can't feign wounds or illness. You can't pretend to be a non-combatant if you are one, and you can't pretend to be a United Nations peacekeeper either. The reasoning is that it is hard to create an atmosphere of mutual restraint for all parties, including civilians, if one side can't believe a word the other side is saying.
Interestingly, though, ruses of war are not perfidious. What ruses of war? Well, things like camouflage and decoys, dummy operations and misinformation, according to the 1977 additional protocol to the Geneva Convention. Kind of makes me wonder how all these distinctions were hammered out.
You'd think that there would be a lot of great quotes on perfidy, and perhaps there are, but the one I liked best was the one at the bottom of the Online Etymology Dictionary entry:
Combinations of wickedness would overwhelm the world by the advantage which licentious principles afford, did not those who have long practiced perfidy grow faithless to each other.