More precisely the Peace of Westphalia, which was a deal between the crowned heads of Europe to stop rocking the boat, and the absolute opposite of what the Enlightenment wanted since it was designed to consolidate royal political control.
After that, the next big wave was the revolutions of 1848, which were inspired by national romanticism, but it’s valid to see that as an evolution of ideas that first arose in the Enlightenment. It certainly wasn’t out of any belief in royal absolutism.
Also I see the Islamic movement in recent years pushing for Islamic homogeneous countries and driving ethnic, religious, language and sexual minorities out of their homelands (mainly into Europe).
Compare to today (often secular) European counterparts Arabic nations are homogenous and root cause was Anti enlightenment ideologies.
The seeds were planted during the enlightenment period but I believe the raise of nationalism is generally considered post-enlightenment