The clash of conservatism and liberalism led to a number of revolutions and attempted revolutions during the early to middle parts of the 1800s. Later in the century, nationalism led to conflicts as what are now Germany and Italy (especially) tried to unify the various little political entities that held people of their ethnic groups.
Especially in the 1840s, there were revolutions around Europe led by liberals who wanted more democracy. The most important of these was the one that occurred in Germany in 1848.
In the 1870s, both Germany and Italy unified. Each of these had been made up of many little "countries." In both cases, the unification caused conflicts to erupt.