The First war of Schleswig (1848 – 1850) was a military conflict in southern Denmark. It also involved troops from Prussia and Sweden.

The Napoleonic Wars had awakened German national feeling, and the political bonds that had historically existed between Schleswig and Holstein suggested that the two regions should form a single country within a united Germany. A counter-movement developed among the Danish population in northern Schleswig and (from 1838) in Denmark itself, where the Liberals insisted that Schleswig had belonged to Denmark for centuries and that the Eider River, the historic border between Schleswig and Holstein, should mark the frontier between Germany and Denmark. The Danish nationalists thus aspired to incorporate Schleswig into Denmark, in the process detaching it from Holstein. German nationalists conversely sought to confirm Schleswig's association with Holstein, in the process detaching the former from Denmark.

These differences led in March 1848 to an open uprising by Schleswig-Holstein's German majority in support of independence from Denmark and of close association with the German Confederation. The military intervention of Prussia helped the rising: the Prussian army drove Denmark's troops from Schleswig-Holstein.

This war between Denmark and Prussia lasted three years (1848–1850) and only ended when the Great Powers pressured Prussia into accepting the London Convention of 1852. Under the terms of this peace agreement, the German Confederation returned Schleswig-Holstein to Denmark. In an agreement with Prussia under the London Protocol of 1852, the Danish government in return undertook not to tie Schleswig more closely to Denmark than to its sister duchy of Holstein.

See also

• Schleswig-Holstein
• Second war of Schleswig