Started a war but got nothing from winning

I have declared a war aginst Pictland but got no territory or anything after winning it. Am I missing something obvious?

Screenshot before war: and before declaring peace:

Solution 1:

This is a war to press someone else's claim on a territory, not for you.

Such claim expands your territory only if one of these three situations happens:

• You are pressing for a title of lower tier (meaning pressing for duke or count titles if you are King of Érie) and the person receiving the title is of your dynasty (meaning same last name with you)
• The territory is your de jure (meaning pressing someone for the county of Dubhlinn when you are King of Érie because Dubhlinn is a de jure county of Kingdom of Érie)
• The claimant already has a landed title in your realm and the contested title is of lower rank than yours (e.g. you claim Duchy of Pictland for the Count of Dubhlinn) (credit to Philipp)

In your case, since you are a king and are pressing for a claim on king title, situation one is not true. Moreover, Kingdom of Pictland is de jure of Empire of Brittany, and you do not have this title, situation two is not true as well.

Good thing is the Queen of Pictland should now be very grateful of you and should easily be formed an alliance with.

Solution 2:

The war was to press someone else's claim

The war declaration tooltip says "When we win the war: ... Princess Elaine of Pictland will gain the Kingdom of Pictland" This option was available because Princess Elaine was in your court and had a claim on Pictland that could be pressed. Notice that any wars declared that are for another character's claims have their portrait next to the coat of arms of the title that the war will be fought over.