Who was fighting in the Crimean War, and for what reasons?
As with any war, there were multiple causes. The proximate cause had to do with allocation of the right to conduct rites and build churches in specific areas of Jerusalem. Ever since the Crusades, there had been a series of uneasy compromises among multiple orthodox patriarchates, Roman Catholics, and various Protestant denominations, with the Ottoman Empire, the secular ruler of the locale, somewhat acting as peacekeeper. As the Ottoman Empire began to crumble, Russian started to assert its authority both in the matter of Jerusalem and in territorial expansion into the Black Sea. France, Britain, and Sardinia sided with the Ottoman Empire against Russia.