Why was Germany unified in 1870

In 1863 the Polish revolt in the Russian part of Poland, further helped Bismarck's cause; the Russian army crushed the revolt with severity, this led to harsh criticism on the part of the French with regard their handling of the Polish affair, and made any future cooperation between the two very unlikely, therefore lessening the chance of a major international coalition being led against Prussia. .
             Bismarck's primary means of achieving German Unity came with the expansion of Prussia's power within the Confederation, this was done not only politically but also in more tangible ways, with the annexation of new lands by Prussia. When in 1863 Denmark attempted to annex the duchies of Schleswig-Holstein, Bismarck was provided with the opportunity to start to realise his aims. The Danish occupation of the duchies was in breach of the Treaty of London signed in 1852; as a result Bismarck acted prudently and skilfully, forcing the Austrians into an alliance. This resulted in a combined Austro-Prussian army advancing but halting at the border of Denmark proper, in accordance with Britain's demand. This move by Bismarck succeeded in maintaining international opinion, and, following the refusal of the Danish King to compromise over the status of Schleswig, thus freeing Prussia from the London Treaty, allowed Bismarck to manipulate the situation to Prussia's advantage. Consequently after the war flared up again in the summer of 1864, the result being that the two duchies were placed under Austro-Prussian control and Bismarck had succeeded in committing Austria to a corner of Germany far from her own territories. The enmity that arose between Austria and Prussia over the Schleswig-Holstein affair was amplified as Bismarck repeatedly provoked Austria with demands that the German Confederation be reformed without Austrian interference.
             Bismarck's political skill surfaced again when his diplomatic manoeuvres persuaded Emperor Napoleon III to remain neutral, playing on his want of land for France, and then by the signing of a treaty with Italy that would commit Austria to fighting on two front in the almost inevitable event of war.