You said the Templars declared war.
A inaccuracy.
The Mages kicked off the fighting, broke out of the circle, prevented any future peace measures and prompted the war.
So its quite directly tied to what you said.
No, I said that they started this whole war. That's not the same as declaring war. And they did. The timeline as I understand it (I haven't read Asunder, so all I have is the wiki) is as follows:
1. The College of Enchanters is disbanded.
2. Knight Commander Eron is removed from power by Lord Seeker Lambert.
3. Lord Seeker Lambert effectively orders Evangeline to destroy the knowledge of the potential cure to the Rite of Tranquility.
4. Divine Justinia is interested in the Tranquility cure; Lambert opposes it on principle.
5. Wynne leaks knowledge of the Tranquility cure; Divine Justinia wishes for a meeting of the College of Enchanters as a Conclave.
6. Lord Seeker Lambert agrees to the meeting on three conditions: (i) All mages but First Enchanters are disenfranchised; (ii) Rhys et al are imprisoned; and (iii) Pharamond is made tranquil again.
7. Divine Justinia, head of of the Chantry, with the consent of Lord Seeker Lambert, lawfully convenes a Conclave of the College of Enchanters. To the extent that anything in Thedas or done by the Chantry can have some kind of legitimacy, the Conclave is legitimate.
8. Lord Seeker Lambert conspires, actively, to suppress knowledge of the cure for the Rite of Tranquility and orders Evangeline to take steps to suppress it.
9. Fionna tables a vote: secession of the Circles of Magi from the Chantry. The motion may well be illegitimate and ineffective. No vote is held, because:
10. Lord Seeker Lambert, with an army at his behest, disrupts the lawfully convened Conclave, and declares their actions as treason. He seeks to arrest Rhys, the mages refuse, and there is violence.
The actual fight that follows is irrelevant. The fact that Lambert had reason to suspect Rhys for murder (the murder weapon being found in his room) is irrelevant. There is no connection, relationship, or basis, to disrupt the Conclave. Lord Seeker Lambert explains directly to Evangeline his motivations: to prevent the mages from pushing for independence, or even for greater freedom, because he believes it will lead to Tevinter.
Now let's look at what I said:
[The templars...] started this whole war over the idea that [the Templars] might not get to be the absolute determinants of life or death over the mages...
Every step that Lambert takes - as much and as far as possible as his authority allows - is to fight and suppress and imprison the mages. That's the basis for his declaration of independence, as well. And it isn't Lambert alone - other templars massacre, for example, Dairsmuird.