Yeah, basically it's around the prohibition Era where governments tried to legislate based upon morals and banned certain substances such as alcohol, this led to crime sky rocketing due to the illegal sale of such products. Gangs were formed and gangsters such as Al-Capone took control of the streets figuratively and somewhat literally. 1920-40 ish.
Nowhere near the present though, I can see how you'd think this with certain modern graphics in the game (modern cars) etc.