The population of Assyria seems to have been more purely Semitic than that of Babylonia. Such at least was the case with the ruling classes. It was a population of free peasants, of soldiers, and of traders. Its culture was derived from Babylonia; even its gods, with the exception of Assur, were of Babylonian origin. We look in vain among the Assyrians for the peace-loving tendencies of the Babylonians; they were, on the contrary, the Romans of the East. They were great in war, and in the time of the Second Assyrian empire great also in law and administration. But they were not a literary people; education among them was confined to the scribes and officials, rather than generally spread as in Babylonia. War and commerce were their two trades.

The Kassite conquerors of Babylonia soon submitted to the influences of Babylonian civilisation. Like the Hyksos in Egypt, they adopted the manners and customs, the writing and language, of the conquered people, sometimes even their names. The army, however, continued to be mainly composed of Kassite troops, and the native Babylonians began to forget the art of fighting. The old claims to sovereignty in the west, however, were never resigned; but the Kassite kings had to content themselves with intriguing against the Egyptian government in Palestine, either with disaffected Canaanites, or with the Hittites and Mitannians, while at the same time they professed to be the firm friends of the Egyptian Pharaoh. Burna-buryas in B.C. 1400 writes affectionately to his "brother" of Egypt, begging for some of the gold which in Egypt he declares is as abundant "as the dust," and which he needs for his buildings at home. He tells the Egyptian king how his father Kuri-galzu had refused to listen to the Canaanites when they had offered to betray their country to him, and he calls Khu-n-Aten to account for treating the Assyrians as an independent nation and not as the vassals of Babylonia.

The Assyrians, however, did not take the same view as the Babylonian king. They had been steadily growing in power, and had intermarried into the royal family of Babylonia. Assur-yuballidh, one of whose letters to the Pharaoh has been found at Tel el-Amarna, had married his daughter to the uncle and predecessor of Burna-buryas, and his grandson became king of Babylon. A revolt on the part of the Kassite troops gave the Assyrians an excuse for interfering in the affairs of Babylonia, and from this time forward their eyes were turned covetously towards the kingdom of the south.

As Assyria grew stronger, Babylonia became weaker. Calah, now Nimrud, was founded about B.C. 1300 by Shalmaneser I., and his son and successor Tiglath-Ninip threw off all disguise and marched boldly into Babylonia in the fifth year of his reign. Babylon was taken, the treasures of its temple sent to Assur, and Assyrian governors set over the country, while a special seal was made for the use of the conqueror. For seven years the Assyrian domination lasted. Then Tiglath-Ninip was driven back to Assyria, where he was imprisoned and murdered by his son, and the old line of Kassite princes was restored in the person of Rimmon-sum-uzur. But it continued only four reigns longer. A new dynasty from the town of Isin seized the throne, and ruled for 132 years and six months.

It was while this dynasty was reigning that a fresh line of energetic monarchs mounted the Assyrian throne. Rimmon-nirari I., the father of Shalmaneser I. (B.C. 1330-1300) had already extended the frontiers of Assyria to the Khabur in the west and the Kurdish mountains in the north, and his son settled an Assyrian colony at the head-waters of the Tigris, which served to garrison the country. But after the successful revolt of the Babylonians against Tiglath-Ninip the Assyrian power decayed. More than a century later Assur-ris-isi entered again on a career of conquest and reduced the Kurds to obedience.

His son, Tiglath-pileser I., was one of the great conquerors of history. He carried his arms far and wide. Kurdistan and Armenia, Mesopotamia and Comagênê, were all alike overrun by his armies in campaign after campaign. The Hittites paid tribute, as also did Phoenicia, where he sailed on the Mediterranean in a ship of Arvad and killed a dolphin in its waters. The Pharaoh of Egypt, alarmed at the approach of so formidable an invader, sent him presents, which included a crocodile and a hippopotamus, and on the eastern bank of the Euphrates, near Carchemish and Pethor, he hunted wild elephants, as Thothmes III. had done before him. His son still claimed supremacy in the west, as is shown by the fact that he erected statues in "the land of the Amorites." But the energy of the dynasty was now exhausted, and Assyria for a time passed under eclipse. This was the period when David established his empire; there was no other great power to oppose him in the Oriental world, and it seemed as if Israel was about to take the place that had once been filled by Egypt and Babylon. But the opportunity was lost; the murder of Joab and the unwarlike character of Solomon effectually checked all dreams of conquest, and Israel fell back into two petty states.

The military revival of Assyria was as sudden as had been its decline. In B.C. 885, Assur-nazir-pal II. ascended the throne. His reign of twenty-five years was passed in constant campaigns, in ferocious massacres, and the burning of towns. In both his inscriptions and his sculptures he seems to gloat over the tortures he inflicted on the defeated foe. Year after year his armies marched out of Nineveh to slaughter and destroy, and to bring back with them innumerable captives and vast amounts of spoil. Western Asia was overrun, tribute was received from the Hittites and from Phoenicia, and Armenia was devastated by the Assyrian forces as far north as Lake Van. The policy of Assur-nazir-pal was continued by his son and successor Shalmaneser II., with less ferocity, but with more purpose (B.C. 860-825). Assyria became dominant in Asia; its empire stretched from Media on the east to the Mediterranean on the west. But it was an empire which was without organisation or permanency. Every year a new campaign was needed to suppress the revolts which broke out as soon as the Assyrian army was out of sight, or to supply the treasury with fresh spoil. The campaigns were in most cases raids rather than the instruments of deliberately planned conquest. Hence it was that the Assyrian monarch found himself checked in the west by the petty kings of Damascus and the neighbouring states. Ben-Hadad and Hazael, it is true, were beaten again and again along with their allies, while Omri of Israel offered tribute to the invader, like the rich cities of Phoenicia; but Damascus remained untaken and its people unsubdued.

The war with Assyria, however, saved Israel from being swallowed up by its Syrian neighbour. Hazael's strength was exhausted in struggling for his own existence; he had none left for the conquest of Samaria. Shalmaneser himself, towards the end of his life, was no longer in a position to attack others. A great revolt broke out against him, headed by his son Assur-dain-pal, the Sardanapallos of the Greeks, who established himself at Nineveh, and there reigned as rival king for about seven years. His brother Samas-Rimmon, who had remained faithful to his father, at last succeeded in putting down the rebellion. Nineveh was taken, and its defenders slain. Henceforth Samas-Rimmon reigned with an undisputed title.