I don't think it starts in 1774, as that would be a total of 8 turns.


If you read the excerpt put up on gamespot

"The Road to Independence sees you taking charge of the foundation of Jamestown as the British, all the way through to acting as Washington and removing the evil tyranny of Britain from the United States. It's a mission-based campaign set within a strong narrative structure that gives a brand-new experience to our established players and new initiates alike."
So you start in 1700, since james town was founded back in 1607. So you start as the British and slowly you become the Colonists.