Hesse-Hanau was a territory in the Holy Roman Empire. It emerged when the former county of Hanau-Münzenberg became a secundogeniture of Hesse-Cassel in 1760. When the reigning count, William IX, also became landgrave of Hesse-Cassel in 1785, the two governments began to merge, although the process was delayed first by French occupation, and later by incorporation into the French satellite duchy of Frankfurt. The incorporation of Hesse-Hanau with Hesse-Cassel was not completed until 1821.