I don’t think it was just money, both dialogue from one of the Samerian emissaries and Iris if you talk to her on the boat after the encounter with the pirates seem to suggest there’s more to it than that. It is possible they’re both just wrong, but narrative wise those are weird lines to put if they are just completely incorrect.
As for what the reason for trying to start a war is if not money, I got nothin’.
Honestly really could’ve been anyone, but my guess is aesir, though that could feel lazy for the story
Simple. money. War = more contracts = more money
It doesn’t make sense for the Order to be behind this since the whole reason this started is because one of their high lords is dead. Meaning it would be in their best interest for this to NOT happen
This seems to be something that has been going on for a while though, even before Calvus died
Occam’s razor dictate that the Syndicate wanted more wars to be waged, leading to them getting contracted more and getting more money in the process.
However, why do they need more money? Sure having a lot of money is great and all, but simple greed can be a mask. A mask for something big. We’ll never know for sure
I will say 2 theories:
1. Money (the realistic theory)
If there’s a war, obviously there are gonna be more assasination contracts, making assasin syndicate wealthier.
If that’s not enough, the war provocation itself could be payed by external source, however this one could be false because the war started without the need of assasin’s provocation (proof in the notes you can see after story-killing Captain Maria.
2. Planned thievery of sea curses of the kingdoms (the wilder theory)
As you already know, every kingdom holds a certain amount of sea curses (it kinda works like a currency). As far as I know, the Assasin Syndicate doesn’t hold any sea curses, and getting one from a direct war is very unlikely to get to their favor. So they came up with this very smart tactic to let the kingdoms tire each other, and then silently steal the curses (this would actually be a wild plot twist if it was incorporated into the story ngl).
This theory was mine if you wonder who’s that crazy enough.
However, the only logical reason to want a war between these two factions is obviously power and influence, I can’t think of any other logical reason.
Accusing MY hitmen of thievery?!
Murderers maybe… but thieves?? Only the time will say…
i kinda agree with the second theory being plausible, if there’s an evil shadow wizard council member in the leadership of the Assassin Syndicate somehere, they’d definitely use their position to incite chaos and murders to make their job of yoinking curses much easier during the free for all
Aren’t the sea curses effectively the nuclear weapons at this point but in Arcane Odyssey? 
kingdom power is measured partially in number of curse users, but their proficiency/elemental range can vary extremely
so while a kingdom could have a couple of curse users, ones that can actually fly or travel distances rapidly (like the glass or king calvus ones) are more like ICBMs, while non-mobile ones have to be transported normally
Nice, thanks for the explanation 