Attempts to localise this song in the Crimean War (or any other specific conflict) seem essentially a waste of time. It is set in the mythical world of conflict between Christian powers (basically Russian) and Islam (basically Ottoman Turk) of the 19th century, and surely that is as close as we need to get. References to the Shah and the Danube in the most standard versions show a vagueness of locality and allegiances: Percy French was drawing on a long tradition of adventure stories, poems, history books, anecdotes and newspaper articles, and came up with a brilliant and enduring parody of the conflicts involved, which is incidentally extremely relevant to the current world political scene. That is surely as far as we need to go.