In Assassin's Creed III, the Boston Tea Party mission takes place in 1773.
The mission recreates the December 16, 1773 protest in Boston, when colonists boarded ships and threw tea into Boston Harbor. In the historical event, the protest opposed the Tea Act and taxation policies associated with British rule. Assassin's Creed III places its protagonist, Connor, inside a fictionalized version of this famous episode.
The Boston Tea Party is an early milestone in the game's American Revolution setting. It occurs before the fighting that begins at Lexington and Concord in 1775, so 1773 is distinct from the year commonly associated with the start of the Revolutionary War. The game blends documented people and events with the fictional Assassin-Templar narrative.
The mission is sometimes confused with the Boston Massacre, which occurred in 1770, or the Declaration of Independence, adopted in 1776. Those are separate historical events represented or referenced in the game's broader chronology.