I love being able to intervene in my rival's wars

This is such a great addition. I'm playing Strasbourg rn, consolidated much of Alsace and declared Lorraine as my rival.

They wanted to seize Freiburg, which I consider in my sphere of influence, so I intervened. We beat them, and afterward I just made a casus belli on Freiburg myself, and now they are my vassal.

It just felt good to "protect" a smaller political entity that I consider to belong in my sphere of influence, just to seize it myself (would have been even better if it was just because of politics, but it’s already very cool).