Ottoman/Russian Balance of Power.
(There were a number of causes for the Crimean War. None of them particularly good. A conflict between Catholic and Orthodox Christians concerning access to the Holy places in Palestine was one. Arguably this was about Ottoman treatment of Orthodox Christians in Ottoman territory which was a concern to Russia. Inept negotiation made the situation worse.
The major players were Britain, France, and Turkey on one side and Russia on the other. Austria played an important diplomatic role. A since extinct country of Piedmont/Sardinia also sent troops.
Russia lost but the bungling on both sides made the war a gong show from the beginning. Arguably the the issues at stake had been decided before the Crimean portion of the conflict even started. The War was by then pointless homicidal idiocy.
It was an important precursor in the next balance of power moves that created Italy and Germany.)
