Integrate Title Charter For Free

As an Emperor you would need the Kingdom (all de jure land) under your full control for it to start to de jure drift into your empire, kingdoms bordering your de jure Empire will start to drift, usually takes 100 years without setting your chancellor to speed it up.

When you are going to war in CK3 and you conquer a duchy that is part of a kingdom, slowly over the process of 100 years will pieces close to the conquered duchy of that kingdom begin to incorporate themselves into your kingdom and become yours de jure.

It is not possible for counties to de jure drift, and so our above example would not see Dorset shift away from the de jure duchy of Wessex. However, duchies can de jure drift from one kingdom to another, as can kingdoms de jure drift from one empire to another.

In general, a title will be assimilated after being controlled for 100 years. The duration required for assimilation is decreased by the Chancellor task "Integrate Title". Every duchy in the game is considered to be part of a specific de jure kingdom.

Click on the empire title, inspect the "Create Title" button's tooltip. It will state exactly what you need. It is always >80% of the de jure counties, and two kingdoms. The required number and general difficulty varies a lot though between different empires.

If there are places that are de jure part of your realm but currently controlled by a neighbor, you can stick your steward there for 4-5 years "convincing" the local populace to demand to be returned to their "rightful" ruler (you, of course).

De Jure literally "By law" in latin. If you own a County (so game-wise a lesser title) within that Duchy that I'm by law (de jure) the owner, I have the right to request you to be my vassal.