One of the ways that nationalism affected Europe were the numerous uprising and riots of the local population that demanded more rights to speak their language and have power over their own affairs. For example, Poland had a number of uprisings that sought to achieve independence of the countries ruling its territory (Russia and Prussia): for example the Greater Poland uprising of 1848.
It is hard to say without looking at your source (textbook or article if you have one associated with this question) but in the most recent studies, it has been Islam.
