How to do call to arms?

[Kan Da]

I started playing this game recently and i noticed that sometimes ai send call to arms notification even though im not their ally/ guarantee their independence/ sign defensive pact with them. I also didnt find this call to arms option in diplomacy. So how to do this call to arms? Does this only happen if my nation is invaded by another?

[Łukasz Jakowski Games]

You can call to arms when declaring war or from the war menu, which you can open by clicking the flag next to the minimap.

How to Enable Calling Vassals/Puppets to War
https://steamcommunity.com/app/2772750/discussions/11/4632610585628920244/

[n1ckstr]

is there a way to call to arms after the war is declared?