The Schleswig-Holstein Question was first brought to a head during the Revolutions of 1848, when, from 1848 to 1851, revolting German-speaking National liberals backed by Prussia fought for the separation of Schleswig and Holstein from Denmark in the First Schleswig War. Though the status quo ante bellum was restored, the conflict lingered on, and on 1 February 1864 Prussian and Austrian troops crossed the Eider, sparking off the Second Schleswig War, after which Denmark had to cede Schleswig and Holstein according to the Treaty of Vienna. After the Austro-Prussian War of 1866, victorious Prussia took control over all Schleswig and Holstein but was obliged by the Peace of Prague to hold a referendum in predominantly Danish-speaking Northern Schleswig, which it never did.[8]