Imagine you where hired by the assassin creed makers to come up with a story, a country that the assassin was in and a time which the assassin lived in for assassin creed 4.
I would make his ancestor a Persian which lived in 540 BC. Dasmond dad uses the animus to go back to 540 BC and find a key to open the robot section of the cave which the ones who came before used to get their conscious in and become immortal. Dasmond dad finds the key gets himself in the robot and goes into the tempolars bulding where all if the leaders are with Juno and he fights with Juno and kills everyone including her by sacrificing himself.
Before the events of Assassin's Creed 3, Desmond learns another secret from one of his ancestors, Matthew Robinson. In the year 1865, Matthew is on the pursuit of the murderer of Abraham Lincoln. But he would soon become involved with a conflict that could reignite the Civil War and bring the Templars one step closer to victory! Can Matthew surrender his obsession for vengance and save a country, yet alone the world? The legacy continues in Assassin's Creed: Warsong!
Six years after the American Revolution, Connor travels to France at request of Marquis de Lafayatte to help him deal with the Templars stirring up the peasant class to rise against the clergy, the nobility and the monarchy. He ends up having to fight Reginald Birch, the Templar who corrupted his father into joining their order, while he must take down the corrupt Revolutionaries who rule over the land with iron fist, even worse than the king before them.