The main causes of the Crimean War were religion, in particular of the Holy sites in Jerusalem — this applied to all major powers, including France, Britain and the Ottoman Empire — and also British foreign policy which was strongly in support of the Ottoman Empire, as the British saw the Turkish lands as a barrier that could halt Russian expansionism. Russia eventually conceded defeat to the alliance of France, Britain, Sardinia and the Ottoman Empire.
The war began in 1853, when Russia invaded the autonomous regions of Moldavia and Wallachia, which resided in the Ottoman Empire.
This was not intended as a direct act of war by Russia. Instead, the Russians hoped to force the Sultan into concessions for Orthodox Christians in the areas, while seeing how the Empire would respond. It was assumed that because other major powers, such as France and Britain, were not on good terms, they would be unlikely to get involved, let alone work together in coming to the aid of Turkey.
Britain, France and Austria-Hungary all regarded the move as either an expansionist threat, or with disdain, with Britain concerned for its merchant activity in the area, and Austria-Hungary fearful of invasion from Russia given that they had crossed the Danube.