What role did nationalism play in European between 1815-1871?

Nationalism played a vital role in uniting the nation-states of Germany and Italy which had previously resisted attempts at unification even though the peoples of various small principalities shared linguistic and cultural traits. Conversely, nationalism played a strong part in ripping up large multi-ethnic empires like Austria-Hungary, Russia, and the Ottoman Empire, with the latter being beset by Greek, Bulgarian, and Serbian independence movements that actually achieved success.