In Assassin's Creed III, the American Revolution setting begins in 1754.
The game opens in the period leading into the French and Indian War, more than two decades before the Declaration of Independence. This early date allows the story to establish Haytham Kenway, the colonial conflict, and the circumstances surrounding his son, Ratonhnhaké:ton, commonly known as Connor.
The campaign then advances through major events of the American Revolutionary era, including the Boston Massacre, the Boston Tea Party, and the Battles of Lexington and Concord. The historical timeline therefore stretches well beyond 1754.
The year 1776 is a common answer because it is associated with the Declaration of Independence, but it is not the game's opening year. Assassin's Creed III uses a broad historical period rather than portraying only the war's most famous final phase.