2K games has created a Civ III mod, HistoriCanada, designed to teach Canadian High School students about the history of Canada. Players can choose between 17 indigenous and European civilizations to learn, and if they like, reshape Canadian history. Although not strictly law-related, this is the first mod I have seen that actually has a purpose (except for Warcraft III's Defense of the Ancients, which is just badass). The educational benefits seems endless, but really, I just wish I could have played games in class...besides Drug Wars.
HistoriCanada: Great Idea, Terrible Name
They should make one for America too, but mod Warcraft to more accurately depict the course of history.