After two centuries for which sources reveal nothing, the Middle Elamite period opened with the rise to power of the Anzanite dynasty, whose homeland probably lay in the mountains northeast of Khuzestan. Political expansion under Khumbannumena (c. 1285-c. 1266 BC), the fourth king of this line, proceeded apace, and his successes were commemorated by his assumption of the title “Expander of the Empire.” He was succeeded by his son, Untash-Gal (Untash (d) Gal, or Untash-Huban), a contemporary of Shalmaneser I of Assyria (c. 1274-c. 1245 BC) and the founder of the city of Dur Untash (modern Chogha Zanbil). In the years immediately following Untash-Gal, Elam increasingly found itself in real or potential conflict with the rising power of Assyria. Tukulti-Ninurta I of Assyria (c. 1244-c. 1208 BC) campaigned in the mountains north of Elam. The Elamites under Kidin-Khutran, second king after Untash-Gal, countered with a successful and devastating raid on Babylonia. In the end, however, Assyrian power seems to have been too great. Tukulti-Ninurta managed to expand, for a brief time, Assyrian control well to the south in Mesopotamia, Kidin-Khutran faded into obscurity, and the Anzanite dynasty came to an end.
After a short period of dynastic troubles, the second half of the Middle Elamite period opened with the reign of Shutruk-Nahhunte (c. 1160 BC). Two equally powerful and two rather less impressive kings followed this founder of a new dynasty, whose home was probably Susa, and in this period Elam became one of the great military powers of the Middle East. Tukulti-Ninurta died about 1208 BC, and Assyria fell into a period of internal weakness and dynastic conflict. Elam was quick to take advantage of this situation by campaigning extensively in the Diyala River area and into the very heart of Mesopotamia. Shutruk-Nahhunte captured Babylon and carried off to Susa the stela on which was inscribed the famous law code of Hammurabi.
Shilkhak-In-Shushinak, brother and successor of Shutruk-Nahhunte’s eldest son, Kutir-Nahhunte, still anxious to take advantage of Assyrian weakness, campaigned as far north as the area of modern Kirkuk. In Babylonia, however, the 2nd dynasty of Isin led a native revolt against such control as the Elamites had been able to exercise there, and Elamite power in central Mesopotamia was eventually broken. The Elamite military empire began to shrink rapidly. Nebuchadrezzar I of Babylon (c. 1124-c. 1103 BC) attacked Elam and was just barely beaten off. A second Babylonian attack succeeded, however, and the whole of Elam was apparently overrun, ending the Middle Elamite period. It is noteworthy that during the Middle Elamite period the old system of succession to, and distribution of, power appears to have broken down. Increasingly, son succeeded father, and less is heard of divided authority within a federated system. This probably reflects an effort to increase the central authority at Susa in order to conduct effective military campaigns abroad and to hold Elamite foreign conquests. The old system of regionalism balanced with federalism must have suffered, and the fraternal, sectional strife that so weakened Elam in the Neo-Elamite period may have had its roots in the centrifugal developments of the 13th and 12th centuries.
Note: The information on this page was found at Britannica.com