The First Schleswig War, also known as the Schleswig-Holstein uprising and the Three Years' War, was a military conflict in southern Denmark and northern Germany rooted in the Schleswig–Holstein question: who should control the duchies of Schleswig, Holstein and Lauenburg, which at the time were ruled by the king of Denmark in a personal union. Ultimately, Denmark proved victorious with the diplomatic support of the great powers, especially Britain and Russia, since the duchies were close to an important Baltic seaway connecting both powers.