In established series, people are bound to attempt to figure out how one game ties into another. In the case of XCOM , you probably won’t want to try and figure that out. It won’t go well if you try to see the XCOM: Enemy Within influence in XCOM 2 , because it turns out whatever you did in that installment probably won’t be considered “canon.”
XCOM 2 begins with the assumption that the humans failed, and aliens won. There is a chance your story didn’t go that way with XCOM: Enemy Within . But when talking to PC Gamer , Firaxis’ Garth DeAngelis says that it’s almost as though there were no events of Enemy Within based on how things are proceeding in XCOM 2 .
This is due to, as DeAngelis puts it, XCOM going “underground.” This means they didn’t get to dabble in genetic alterations or fancy tech. Instead, your team in XCOM 2 will be scrappy, come November 2015. They’ll be working with what they can, and hoping to loot fallen Advent in time to collect useful upgrade parts before they self-destruct.
Source: PC Gamer