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In page Schleswig-Holstein:

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British attempts to mediate in the London Conference of 1864 failed. With the peace Treaty of Vienna (1864), Denmark was forced to cede Schleswig to Prussia and Holstein to Austria. The two victors divided the duchies despite their casus belli being the defence of the German-speaking Schleswig-Holsteiners' wish to remain unified. But the division did not last long, since Prussia annexed Holstein in 1867, after its victory in the Austro-Prussian War.[citation needed]