The Crimean War was also significant because Austria-Hungary, though not much of a belligerent, turned on Russia which left them without allies when facing Prussia in 1866 and of course the two Empires were critically still enemies when the Archduke was assassinated.
One can keep going backwards in history with cause and effect, but for the two points above, I like to see the Crimean War as the turning point of the European alliances that were in place at the start of "the Great War".