- "Sometime during the Seven Years' War the Templars made their move and destroyed [the Colonial Brotherhood] during the Assassin witch hunt."
- ―Shaun Hastings on the purge, 2012.[src]
Before Haytham arrived in the colonies, the Colonial Assassins under the Mentor Achilles Davenport controlled the Atlantic coast of North America. They used gangs as enforcers, and ruled a number of forts and settlements. The Assassins also possessed an established network of spies and allies. As such, they were superior to the Templars in the colonies. In 1752, the high-ranking Templars Lawrence Washington, Samuel Smith and James Wardrop, were assassinated after stealing the Precursor box and Voynich manuscript from the Assassins in Saint-Domingue, following an earthquake a year prior.
In 1754, following Haytham's arrival in the New World, and the formation of an independent Colonial Rite, the resurgent Templars quickly came into conflict with the well-established Assassins. Beginning as a proxy war between the Templars and mercenaries recruited by the Assassins, the conflict escalated when the two factions sided with opposing European powers during the Seven Years' War.
Turning the tide
From 1757 onward, Shay Cormac, a former Assassin, helped the Templars track down and kill several of his former comrades, including the high ranking Assassins Kesegowaase, Hope Jensen, and Chevalier de la Vérendrye. In addition to his former colonial brothers, Shay also eliminated Adéwalé, a legendary member of the Caribbean branch of the Brotherhood.
Shay also used his ship, the Morrigan, to cripple the Assassin navy. Among the ships which fell victim to his actions were Adéwalé's vessel, the Experto Crede, and the Gerfaut captained by Chevalier de la Vérendrye. Shay also managed to sink the Storm Fortress, the flagship of the Assassin navy.
Furthermore, Shay also eliminated seven Assassin-allied gangs in New York, liberated several forts in the River Valley and along the Atlantic coast, intercepted several Assassins during their missions, and killed a number of stalkers sent after him personally, weakening the Assassin presence further.
In 1760, in a battle at a Precursor Temple in the Arctic, the Brotherhood's leadership was broken. The high-ranking Assassin Liam O'Brien was killed, and the Mentor Achilles Davenport was crippled by Haytham. Thereafter, the balance of power in the Colonies tipped in favor of the Templars, and the Brotherhood was soon on the brink of destruction. Confident that he was no longer a threat, the Templars spared Achilles' life, on the condition that the Assassins stop searching for First Civilization sites.
In 1763, three years after the Assassins' defeat at the Arctic, the Templars launched their final attack on the Davenport Homestead, killing all the remaining Assassins, with the exception of Achilles and Robert Faulkner. Convinced that the lone Mentor no longer posed any threat, the Templars spared Achilles' life once again, this time on the condition that he give up his life as an Assassin.
However, some Assassins survived the purge, such as Benjamin Tallmadge who went into hiding, or Pierre Bellec who was training in the colonies, but left for France shortly before the attack happened. After having spent six years in isolation at the manor until the arrival of Haytham's son, Ratonhnhaké:ton, Achilles decided to train the boy, beginning to rebuild the Colonial Brotherhood.