Hi.
I will tell you a story. Saxony was Austrian vassal. England, Austrian ally (and a leader of alliance) dowed Saxony, but Austria dishonoured. Then immediately England invites Austria to join the alliance again, on which Austria agrees. It automatically joins a war with Saxony, but it doesn't break a vassalage. And - tada - it is at war with its vassal.
Austria assaults Sachsen and annexes it shortly after.
I will tell you a story. Saxony was Austrian vassal. England, Austrian ally (and a leader of alliance) dowed Saxony, but Austria dishonoured. Then immediately England invites Austria to join the alliance again, on which Austria agrees. It automatically joins a war with Saxony, but it doesn't break a vassalage. And - tada - it is at war with its vassal.

Austria assaults Sachsen and annexes it shortly after.
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