The Assyrian monarchs wrote constantly of internal danger, fear of palace intrigue, and feared a rebellion. Upon the death of Ashurbanipal, a series of bitter and bloody wars of succession occurred, weakening the empire – from 625 BC onward, the empire's domination over the Middle East, Asia Minor, Caucasus and East Mediterranean gradually began to fade. An alliance formed between external states, such as the Chaldeans, who took advantage of the upheavals in Assyria to take control of much of Babylonia with the aid of the Babylonians themselves. This precipitated the Neo-Babylonian Empire, whose goal was the overthrow of the Neo-Assyrian Empire, seize the capital Nineveh, and transfer the seat of Mesopotamian power to Babylon. Nineveh was not only a political capital, but home to one of the great libraries of Akkadian tablets and a recipient of tribute from across the near east, making it a valuable location to sack. The Assyrian chronicles end abruptly in 639 BC after the destruction of Susa, the capital of Elam, and the subjugation of a rebellious Babylon ruled by Ashurbanipal's own brother Shamash-shum-ukin. Business records are missing after 631 BC. The primary sources are written afterwards by a victorious Neo-Babylonian from the reign of Nabopolassar. The primary chronicle is numbered 21901, which was translated by C. J. Gadd in 1923, and can be found in the British Museum. By the Babylonian tradition set down by Herodotus much later, a Hebrew tradition attributed to Nahum, and by reference in Egyptian chronicles, all were hostile to Assyria. There are also legends that have grown up in the centuries afterwards, among peoples who descend from one of the involved nationalities, including the still Mesopotamian Eastern Aramaic speaking and Christian Assyrians of northern Iraq, southeast Turkey, northwest Iran and northeast Syria. The Medes were ruled by King Cyaxares. Although initially defeated by the Assyrians, he rebuilt his army and attacked Nineveh in conjunction with other warring factions. One of the recountings of the actual battle is taken from the excerpts of "Persica", written by Ctesias, preserved in Diodorus Siculus and Photius, whose account may have been mixed with accounts of other battles. According to a babylonian clay tablet discovered in the 19th century named Fall of Nineveh Chronicle, there was a bitter 12-year struggle between Babylon and Assyria, as well as civil wars in Assyria itself.