Tsar Nicholas I of Russia, based on his role in suppressing the revolutions of 1848 and his mistaken belief that he has British diplomatic support, moves against the Ottomans, who declare war in 1853.

Thus the Crimean War begins, but the European powers are frightened of Russia, and in 1854 Britain, France, and Sardinia join the Ottoman Empire against Russia.

Austria offers the Ottomans diplomatic support, while Prussia remains neutral.

The European allies land in Crimea and lay siege to a well-fortified base at Sevastopol'.

After a year's siege the base falls, exposing Russia's inability to defend a major fortification on its own soil.

Nicholas I dies before the fall of Sevastopol', but even before then he had recognized the failure of his regime.

Russia now has to initiate major reforms or cease to be a competitive major power.

Austrian Neoabsolutism, with its aim of creating a unified, supranational state, runs counter to the prevailing European trend.

The empire's peoples cannot be isolated from the larger nationalist struggles of the German, Italian, and Slavic peoples.

In Hungary, active resistance to the Austrian government declines, but passive resistance grows.

During the Crimean War (1853-56), the situation in Hungary makes Austria vulnerable to economic and political pressure from Britain and France, the allies of Turkey against Russia.

Thus, when Russia asks for Austria's support, Austria initially seeks to mediate the conflict but then joins the western allies against Russia.

By failing to repay Russia for its help in Hungary in 1849, Austria loses critical Russian support for its position in Germany and Italy.

France takes advantage of the estrangement between Austria and Russia to set up a military confrontation between Austrian and Italian nationalist forces.

This opens the door to French military intervention in support of the Italians in 1859.

Because Franz Joseph is unwilling to make the concessions that are Prussia's price for assistance from the German Confederation and because he fears the French might stir up trouble in Hungary, Franz Joseph surrenders Lombardy in July 1859.

Russia withdraws from Wallachia and Moldavia in 1851 but returns yet again in the summer of 1853, thus precipitating the Crimean War.

In 1854 Franz Joseph and the sultan force Tsar Nicholas I to withdraw his troops from the principalities, and imperial and Ottoman soldiers soon occupy them.

Russia's defeat in the Crimea forces the tsar to seek peace, affirmed in 1856 by the Treaty of Paris.

De jure Ottoman suzerainty over the principalities continues after the treaty, which abolishes the Russian protectorate and replaces it with a joint European guarantee.

The treaty also frees navigation on the Danube and forces Russia to cede part of southern Bessarabia, which includes control of the river's mouth, to Moldavia.

The Kingdom of Sardinia becomes an ally of Britain and France in 1855 in the Crimean War, giving Cavour's diplomacy legitimacy in the eyes of the great powers.