War

It's painful for pan-monarchists (a very different worldview from that of nationalists loyal to one particular monarchy) to contemplate the fact that quite a bit of European history from the Middle Ages up until 1918 consisted of monarchies going to war with each other, though less so from 1783 to 1914 (if the Bonaparte emperors are not counted as proper monarchs). Only since 1945 have Europe's remaining monarchies generally enjoyed good relations with each other. But it is clear, and may become clearer still in the 21st century, that getting rid of most of the monarchies did not make things any better and in many ways made them worse.