The First Schleswig War (1848-1851) was a conflict between the Kingdom of Denmark and the German states, primarily over the duchies of Schleswig and Holstein. The war began when nationalist movements in these duchies sought to unite with Germany, leading to a rebellion against Danish rule. The conflict saw Danish forces fighting against a coalition of German volunteers and troops from the German Confederation. The war ended with the Treaty of Berlin in 1851, which restored Danish control over Schleswig and Holstein, but tensions remained, setting the stage for future conflicts in the region.