In Assassin's Creed III, the American Revolutionary War storyline begins in 1754.
The game's opening date places the player in the French and Indian War, the North American conflict that began in 1754. The early chapters follow Haytham Kenway before the narrative later introduces Ratonhnhaké:ton, known as Connor. This structure shows the political and family circumstances that lead into the American Revolution.
The main revolutionary period is usually associated with events from 1775 onward, including the Battles of Lexington and Concord. Those later dates are important in the game, but they are not the beginning of its overall historical storyline. Assassin's Creed III deliberately starts decades earlier to establish its characters and the colonial conflict.
The war ending in 1783 is another tempting answer because the Treaty of Paris concluded the American Revolutionary War that year. The correct date for the game's opening historical setting is 1754, the start of the French and Indian War.