Ubisoft's barbarism of Vikings in Europe. It's safe to say that the series has given the industry plenty of historical settings to explore.
Yet, there's still hanging fruit that Ubisoft should take advantage of. For example, many fans voiced their interest in Feudal Japan as an Assassin's Creed setting, but other companies pounced first, launching a series of samurai games like Sekiro: Shadows Die Twice and Ghost of Tsushima.
Because history is so complex and diverse in conflict and culture, there's a lot of time periods and settings that Assassin's Creed has yet to tackle. The following Assassin's Creed locations are just hopes and dreams for Ubisoft's future, but they pack the most potential as well.
Assassin's Creed Set In Feudal Japan
As said before, games like Sekiro and Ghost of Tsushima covered this era with great precision, though the latter is closer to an Assassin's Creed game than the former. Despite this era being an occupied setting already by a number of action-adventure titles, there's much that can be salvaged and played out differently here. For example, seeing the end of the samurai-era and the westernization of Japan.
Assassin's Creed Set In World War 1
Modern warfare would be a difficult task for the franchise, but the Great War takes place between the times of old-era tech and the beginning of a new kind of warfare. Swords were still used, but so were early machine guns. Soldiers used horses, but they also used airplanes and tanks. An assassin using the trenches or the cover of a massive battalion charge could prove interesting for the format. It's also a conflict not widely explored in the gaming industry, especially when compared with the Second World War, so there's a lot of ground to cover if the next Assassin's Creed game was set in WW1.
Assassin's Creed Set In Ancient Rome
Yes, Rome was a setting for a previous Assassin's Creed game, but going even further back in the timeline would change the location drastically. Imagine taking part in arena gladiator fights or in a large-scale battle among the Roman ranks. The Roman Empire's reign was long and filled with interesting characters, and provides a lot of material for potential Assassin's Creed shenanigans.
Assassin's Creed Set In The Mongolian Empire
Ubisoft could take the alternate route of Ghost of Tsushima and place the protagonist on the opposite side of the conflict. This would allow them to explore similar time periods and areas as that title but allow for less creative overlap with Sucker Punch's recent release.
An Assassin (or a Templar) fighting in the ranks of Genghis Khan, or even hunting him, would make for an intriguing story.
Assassin's Creed Set In The American Civil War
Due to the divisive nature of the Civil War, the storyline and conflict would be provocative and rather difficult to translate in an appropriate manner. All of the emotional tension surrounding the Civil War does beg the question, however: what would a protagonist do if their next target were Abraham Lincoln? Not many games have trekked into this territory, and if Assassin's Creed's developers do it properly it could be an intriguing and interesting alternate history setting for the series.
Assassin's Creed Set During Prohibition
Getting a little closer to the modern era, setting a new Assassin's Creed game during Prohibition would allow players to explore the fight between the mob and the police. Although many would likely worry the game would reflect the Mafia series or Grand Theft Auto, the assassin elements could be innovative enough to keep it fresh. The protagonist's efforts could pit both sides against each other, making for a slick and stylized experience dotted with rum raids and leaping from rooftops.
Assassin's Creed Set In A Dystopian Future
Set centuries ahead of the current era, a dystopian future Assassin's Creed setting would be a great opportunity to refresh the series. With little-to-no guns, resources, or food thanks to shortages, an assassin using melee weapons crafted from the world around them would be a great restart. There really is no limit to the amount of settings and time periods Assassin's Creed could set itself in if it begins moving forward into the future.