A little while ago I developed an interest in the history of cocktails. I purchased a copy of Ted Haigh's Vintage Spirits and Forgotten Cocktails (deluxe edition, no less) and quite enjoyed it. The book traces the genesis of the cocktail, what happened during prohibition, the war years, the rise of vodka (and near demise of aged spirits) in the 70s, and the current revival of these intoxicating creations. My interest pretty much stopped there, though, since to become a true devotee of the hobby, you need to buy about 30 trillion dollars worth of different types of booze, and kiss your liver goodbye if you want to try and make all of them -- well, I guess you could make them and not try them, but where's the fun in that?! Still, it's a nice reference to have on hand, and I have developed a fondness for the Sidecar and its cousins.
The Sidecar belongs to a category of drinks that Gary Regan (in The Joy of Mixology) calls the New Orleans Sours. This is because they are based on a drink called the Brandy Crusta that was created around 1860 in, you guessed it, New Orleans. These sours are all made from a base spirit, lemon or lime juice, and an orange liqueur. It is the use of orange liqueur instead of sugar syrup that distinguishes the New Orleans Sours from the standard ones like the Whiskey Sour.
Now, if that were the whole story, you'd probably think it's pretty boring (you still may after this, but at least I tried). What I found interesting is that the Sidecar branched off and evolved into something we all know, the Margarita. (The original version of the Margarita, mind you, not the boozy green snowcone most of us are familiar with at the local Tex-Mex joint.)