When Hittite king Šuppiluliuma I (r. c. 1344–1322 BC) conquered Mitanni, he created two provinces (Aleppo and Carchemish), and distributed the large part of territories of this kingdom between his allies. The rest of what had been the empire of Mitanni retained its independence as a Hittite vassal state called Ḫanigalbat. During the reign of the Hittite king Mursili III (better known as Urḫi-Tešub), Ḫanigalbat was conquered by the Assyria Empire and the Assyrians controlled the East bank of the Euphrates.The ‘Eternal Treaty’ from the Hittite perspective pp.3-4 by Trevor Bryce When Ḫattusili III ousted his nephew Urḫi-Tešub and seized the Hittite throne, he had to be content with the permanent loss of Ḫanigalbat to the Assyrians despite its former status as a Hittite vassal state.
