After the conservative rule of Enlil-nirari and Arik-den-ili, the next major expander of the Assyrian state as Adad-Nirari (c. 1307-1275). According to his victory stele (reference), he succeeded in subjugating the Mitanni, making it into a vassal state. Later, after revolts led first by Shattuara and then his son Wasashatta, he devastated much of the area, looting principle Mitanni cities like Washukannu and Hurra (reference),gutting out the capital city of Taidu, and imposing corvee labor on some of the population.
With this important victory behind him, Adad-nirari set his sights further westward. In an attempt to reduce tension with his new neighbor the Hittites, he sent a letter to King Muwatalli, addressing him as brother and requesting access to the Amanus mountains within his territory (Kuhrt pg. 354). The Hittite's reply was much less diplomatic than the Egyptians'. (CTH 171).