The first years of Shamshi-Adad's reign saw a serious struggle for the succession of the aged Shalmaneser.
The revolt was led by Shamshi-Adad's brother Assur-danin-pal, and had broken out already by 826 BC. The rebellious brother, according to Shamshi-Adad's own inscriptions, succeeded in bringing to his side 27 important cities, including Nineveh. The rebellion lasted until 820 BC,[6] weakening the Assyrian empire and its ruler; this weakness continued to reverberate in the kingdom until the reforms of Tiglath-Pileser III.
Later in his reign, Shamshi-Adad campaigned against Southern Mesopotamia, and stipulated a treaty with the Babylonian king Marduk-zakir-shumi I.
In 814 BC, he won the Battle of Dur-Papsukkal against the Babylonian king Marduk-balassu-iqbi, and a few Aramean tribes settled in Babylonia. The extent of Shamshi-Adad's victory was such that he obtained the submission of the Babylonian king and, after obtaining booty from several Babylonian cities, he returned to Assyria with palace treasures and gods (i.e. the sacred representation of the gods).[7]