Hesse-Nassau was a historical region in central Germany, formed in the 19th century. It combined parts of the Grand Duchy of Hesse and the Duchy of Nassau. This area was known for its diverse landscapes, including forests and rivers, and played a significant role in the economic development of the region. In 1866, Hesse-Nassau became part of the Kingdom of Prussia after the Austro-Prussian War. The region's integration into Prussia marked a significant shift in its political landscape, leading to changes in administration and governance. Today, the legacy of Hesse-Nassau can still be seen in the cultural and historical influences in the area.