Nassau-Usingen was a small German principality located in the region of Hesse. It emerged in the early 19th century when the Principality of Nassau was divided into several smaller territories. Nassau-Usingen was known for its picturesque landscapes and small towns, contributing to the cultural heritage of the area. The principality existed until 1866 when it was annexed by the Kingdom of Prussia during the Austro-Prussian War. This incorporation marked the end of Nassau-Usingen as an independent entity, and its territory became part of the larger Prussian state, influencing the political landscape of modern Germany.