Does the difference in treaties between kings and the People of the Book contradict the hadith: (The dhimmah of the Muslims is one, and the lowest of them upholds it)?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: Ibn al-Qayyim (may Allah have mercy on him) stated that if there is a treaty between some Muslim kings and some of the People of the Book, it is permissible for another king who has no treaty with them to wage war against them. So how do you reconcile this with the saying of the Prophet (peace and blessings be upon him) that ?

Answer:
Their dhimmah is one if they are under a single authority, my brother. If they are under a single authority, their dhimmah is one. But if they are separate states, as is the case now, then each state has its own ruling. Yes, and this is the consensus of the Muslims. After the fall of the Abbasid state, the Muslims became separate states and kings, each state having its own ruling, and it is not required for one state to act according to the ruling of another state.