How do truces work?

My Empire is rivaling a neighbouring weaker Empire, let's call it Empire A, who has a defensive pact with Empire B, a much larger Empire. I recently had a war against Empire B, which ended in a truce. I plan to vassalise Empire A in order to secure my borders from invasion. However, this may cause a war against both Empire A and Empire B, a conflict I wish to avoid, due to their defensive pact. Will my war against Empire A lead to war against Empire B due to their defensive pact, despite the truce between my Empire and Empire B?

I know that truces take place after a war between two belligerents and prevent conflict between them for 10 years, but I wonder if it's possible for a Human player and the AI to break them. Also, I want to the repercussions of breaking a truce.

Solution 1:

No, in all Paradox games truce only prevents (or penalizes) the attacker's actions. Defenders get called to war even if the truce is still in place.

So yes, you'll get a war with both empires.

And at the current version of the game it's impossible to truce-break and attack. You have to target some other party, that'll drag you main goal into the war