The story begins here. The previous week begins here.
The Greeks had learned from the Kadlandithar, and now the Kadlandithar learned from the Greeks. The Kadlandithar learned to raid and pillage. They learned to be slavers. And they learned to worship Poseidon and pray to him as though he cared anything about their daily lives.
And by raiding and enslaving their brothers, the Kadlandithar became a stench to the Aghianar and the Aghianar determined to annihilate them for the treason of a brother is more bitter than the hatred of an enemy.
As for Azdior, he cared nothing for worship; to him humans were nothing but allies and trading partners. But Azdior despised Poseidon, holding Poseidon in contempt for the weakness of craving the attention and worship of lesser creatures like humans. It perhaps would have meant little to Azdior if Kadlandith had merely stopped trading with him in preference for another Rhodonaar prince, but to leave Azdior for Poseidon and worse, to give Poseidon the worship that he craved, this infuriated Azdior.
And was not a sweet temper that caused Azdior to be known as the Bull God.