In Assassin's Creed III, the modern-day story begins in 2012.
The modern-day sections follow Desmond Miles and his allies as they prepare for a catastrophe linked to the end of the Mayan calendar's 13th baktun. The opening modern-day material takes place shortly after the events of Assassin's Creed Revelations and leads into Desmond's effort to use the Animus to find information needed to protect Earth.
The historical campaign is set much earlier, mainly during the American Revolutionary War, and follows Ratonhnhaké:ton, also known as Connor. That historical setting can make the game's chronology confusing. Assassin's Creed III alternates between the 18th-century memories experienced through the Animus and the 2012 present-day storyline, which is part of the series' continuing modern conflict between Assassins and Templars.