Assyrian religion was Mesopotamian religion with one substitution. The pantheon, the temple economy, the divination and the incantation literature were substantially shared with Babylonia, but at the head of it stood Ashur, who was the city of Ashur before he was a god and who has almost no mythology of his own. Assyrian scribes solved that by rewriting. The Babylonian creation epic Enuma Elish was recopied in the north with Ashur in Marduk's place, which is as clear a statement of religious politics as the ancient Near East produced.
The king was the god's steward rather than a god himself, and his campaigns were reported to Ashur in letters deposited in the temple. This is why the royal inscriptions read as they do. Conquest is presented as the extension of the god's order over territory that lay outside it, and the deportation of whole populations is described in the same register.
Divination carried the weight of state decision. The Nineveh libraries preserve extispicy queries, astrological omen series and the dream compendium known as the Assyrian Dream Book, alongside the letters of scholars advising Esarhaddon and Ashurbanipal on when to act and when to wait. Nicole Brisch's survey of Mesopotamian deities sets Ashur beside Ishtar of Nineveh and Ishtar of Arbela, the two goddesses whose oracles spoke most directly to those kings.