History of germany

Schleswig-Holstein: 1848-1864
The region of Schleswig-Holstein, at the interface between German and Danish-speaking regions but with no clear geographical boundaries, is a natural place for conflict in an era of growing nationalism. Historically Holstein has been within the German empire and Schleswig outside it, but both duchies have been attached to the Danish crown since 1460.
In the excitement of 1848 a revolutionary group seizes Kiel, declares the independence of the two duchies from Denmark and appeals to theGerman Confederationfor help. The result is an invasion of Schleswig-Holstein, and then of Denmark itself, by a Prussian army on behalf of the Confederation. 
On this occasion international pressure forces the Prussians to withdraw and the two duchies are restored to Denmark. But the crisis flares again in 1863 when the Danish king Frederick VII dies. He has no direct male heir. In Denmark the crown can pass through the female line; but Holstein, like the rest of the German empire, observes theSalic law.This casts doubt on the right of the new Danish king, Christian IX, to the duchy of Holstein. TheGerman Confederation(still officially presided over by Austria) decides to act. A joint Austrian and Prussian army overruns both Holstein and Schleswig. The result this time is that the two duchies are ceded jointly to Prussia and Austria, by the treaty of Vienna in October 1864. 
At the best of times agreement on how to administer the new territories would be difficult to achieve between Prussia and Austria, as rivals for hegemony in Germany. It is made more so now by the fact that Prussia has an agressive and skilful new prime minister, Otto von Bismarck, appointed by William I in 1862. He is determined that Prussia shall replace Austria as leader of the German states, and he sees his chance in Schleswig-Holstein.
It is agreed in 1865 that Prussia will administer Schleswig while Austria will be responsible for Holstein.
Austria, presiding over the German Confederation (a role acquired half a century earlier at the congress of Vienna), proposes that the Confederation as a whole should restrain its belligerent member. Prussia, certain to be outvoted on the issue, responds on 14 June 1866 by declaring the Confederation defunct.
On June 15, when Saxony, Hanover and Hesse-Kassel refuse to give assurances that they will remain neutral, Prussia invades all three states. The war deciding the future shape of Germany has begun. It will be a short one.