If you played the previous games - or even if you didn't! - you can set up your own world state at the Dragon Age Keep website - handily found at https://dragonagekeep.com/- and import it into a new game.
There a lot of dialogue differences that depend on what choices you make in the Keep, as well as some operations for the War Table. You can change things such as who the ruler of Ferelden is, and whether Hawke sided with the Templars or the Mages at the end of DA2.
If you haven't played the previous games, I'd suggest completing Inquisition with the default world state first. Then if you want to see how things change on a second run, you can go play around with the Keep.