Secure the High Kingdom of the North Sea: What does "England must be departitioned" mean?

I am playing Crusader King 3 with the Northern Lord flavor pack. There is a decision to "Secure the High Kindom of the North Sea".

One requirement reads:

• The Danelaw currently has De Jure Counties, and England must be departitioned first

I am currently King of Norway, Denmark, and England as well, trying to hold it for 30 years. Now I realize I also have to fullfill that requirement and I have no clue what it entails.

What does departitioning England mean? (The Danelaw already exists. I am fighting with them for the North Sea Heartlands as well.)

The requirement means:

• England must have had a de jure partition split, meaning the Danelaw and England coexist
• afterwards you still have to usurp the remaining Danelaw. (I conquered England when the Danelaw existed already. I don't know if it could work with conquering England as an Danelaw King)

Once I conquered all of the remaining Danelaw territory, an event appeared proclaiming that the Danelaw title was destroyed and all Danelaw claimants lose their claim, only England remains.