He was succeeded by his son, Tukulti-Ninip I, who was the most powerful of the Assyrian monarchs of the Old Empire.  He made great conquests in the north and east, extended and strengthened Assyrian influence in Mesopotamia, and penetrated into Hittite territory, bringing into subjection no fewer than forty kings, whom he compelled to pay annual tribute.  It was inevitable that he should be drawn into conflict with the Babylonian king, who was plotting with the Hittites against him.  One of the tablet letters found by Winckler at Boghaz Koei is of special interest in this connection.  Hattusil advises the young monarch of Babylonia to “go and plunder the land of the foe”.  Apparently he sought to be freed from the harassing attention of the Assyrian conqueror by prevailing on his Babylonian royal friend to act as a “cat’s paw”.

It is uncertain whether or not Kashtiliash II of Babylonia invaded Assyria with purpose to cripple his rival.  At any rate war broke out between the two countries, and Tukulti-Ninip proved irresistible in battle.  He marched into Babylonia, and not only defeated Kashtiliash, but captured him and carried him off to Asshur, where he was presented in chains to the god Ashur.

The city of Babylon was captured, its wall was demolished, and many of its inhabitants were put to the sword.  Tukulti-Ninip was evidently waging a war of conquest, for he pillaged E-sagila, “the temple of the high head”, and removed the golden statue of the god Merodach to Assyria, where it remained for about sixteen years.  He subdued the whole of Babylonia as far south as the Persian Gulf, and ruled it through viceroys.

Tukulti-Ninip, however, was not a popular emperor even in his own country.  He offended national susceptibilities by showing preference for Babylonia, and founding a new city which has not been located.  There he built a great palace and a temple for Ashur and his pantheon.  He called the city after himself, Kar-Tukulti-Ninip[412].

Seven years after the conquest of Babylonia revolts broke out against the emperor in Assyria and Babylonia, and he was murdered in his palace, which had been besieged and captured by an army headed by his own son, Ashur-natsir-pal I, who succeeded him.  The Babylonian nobles meantime drove the Assyrian garrisons from their cities, and set on the throne the Kassite prince Adad-shum-utsur.

Thus in a brief space went to pieces the old Assyrian Empire, which, at the close of Tukulti-Ninip’s thirty years’ reign, embraced the whole Tigro-Euphrates valley from the borders of Armenia to the Persian Gulf.  An obscure century followed, during which Assyria was raided by its enemies and broken up into petty States.

The Elamites were not slow to take advantage of the state of anarchy which prevailed in Babylonia during the closing years of Assyrian rule.  They overran a part of ancient Sumer, and captured Nippur, where they slew a large number of inhabitants and captured many prisoners.  On a subsequent occasion they pillaged Isin.  When, however, the Babylonian king had cleared his country of the Assyrians, he attacked the Elamites and drove them across the frontier.