The history, Of course my version coming up later!

hicken Marengo is a French savoury dish, so named for being the dish that Napoléon Bonaparte ate after the Battle of Marengo.
According to tradition Napoleon demanded a quick meal after the battle and his chef Dunand was forced to work with the meager results of a forage: a chicken (and some eggs), tomatoes, onions, garlic, herbs, olive oil, and crayfish. The chef cut up the chicken (reportedly with a sabre) and fried it in olive oil, made a sauce from the tomatoes, garlic and onions (plus a bit of cognac from Napoleon's flask), cooked the crayfish, fried the eggs and served them as a garnish, with some of the soldier's bread ration on the side. Napoleon reportedly liked the dish and (having won the battle) considered it lucky. He refused to have the ingredients altered on future occasions even when his chef tried to omit the crayfish.
Modern versions of the dish are made by first flouring then browning chicken portions in oil or butter. The partly cooked chicken is then transferred into a tomato sauce (usually made with onions, garlic, wine & chopped tomatoes). The whole is then cooked slowly until the chicken is done, and a few minutes before serving, a good amount of chopped herbs and black olives are added. This would usually be eaten with a potato dish of some sort, or just crusty bread.