Which Assassin's Creed game first introduced the city of London as its main setting?

Assassin's Creed Syndicate first introduced London as its main setting.

Released in 2015, Syndicate is set in London during the Industrial Revolution, particularly in 1868. Twin protagonists Jacob and Evie Frye fight to weaken Templar control while building an Assassin presence across the city. The campaign includes districts such as Westminster, the City of London, and Southwark.

The game's London is a large open-world interpretation rather than a complete historical reproduction. It includes factories, railways, crowded streets, and landmarks associated with Victorian Britain. Assassin's Creed Unity is set in Paris during the French Revolution, while Rogue focuses on the North Atlantic and parts of North America. Those different settings make them common alternatives to Syndicate in this question.