It is possible to declare war on yourself and your allies, with the help of your allies. If that makes sense. The war end as soon as it start though, so I guess it's kinda minor, unless some AI do it over and over for some reason, or it is abused for some yet to find exploit.
Anyway, how to reproduce :
-declare war on an allied vassal
Apparently, that's all you need.
Here is the screenshot :
As you can see, I'm able to add my capital to the war goal, I was able to confirm and start the war.
Anyway, how to reproduce :
-declare war on an allied vassal
Apparently, that's all you need.
Here is the screenshot :
As you can see, I'm able to add my capital to the war goal, I was able to confirm and start the war.