On 17 July 1806, upon the dissolution of the Holy Roman Empire, the principalities of Nassau-Usingen and Nassau-Weilburg both joined the Confederation of the Rhine. Under pressure from Napoleon, both principalities merged to become the Duchy of Nassau on 30 August 1806, under the joint rule of Prince Frederick August of Nassau-Usingen and his younger cousin, Prince Frederick William of Nassau-Weilburg. As Frederick August had no heirs, he agreed that Frederick William should become the sole ruler after his death. However, Frederick William died from a fall on the stairs at Schloss Weilburg on 9 January 1816 and it was his son William who later became duke of a unified Nassau.
The sovereigns of this house afterwards governed the Duchy of Nassau until 1866. Since 1890, they have reigned over the Grand Duchy of Luxembourg.
^Louda, Jiri; Maclagan, Michael (December 12, 1988), "Netherlands and Luxembourg, Table 33", Heraldry of the Royal Families of Europe (1st (U.S.) ed.), Clarkson N. Potter, Inc.
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