The period from 1914 to 1945 was only 31 years, and yet it contained the two worst conflicts in the history of humanity. World War One lasted for four years and was the first great war in history not only to touch most of the world's nations - whether on their territory or at least involving some forces from them - but also to fear industrialized warfare. It wiped out a generation of young men and laid waste to a continent.
World War Two spanned 1939 to 1945 and was even worse, killing the best part of 100 million people in not just the first fully industrialized war, but also the first fully mechanized genocide in the form of the Holocaust.
What is less understood about these wars is that they are brackets around a pivot in human history, a kind of culmination of the Enlightenment's struggle against the forces of monarchy and imperialism that in some form or another, had stood athwart every society since Roman times.
In the first Great War - as it was then known - empires fell, from the Austro-Hungarian to Tsarist Russia to the Ottomans. This created a vacuum that democracy, with its still relatively new-fangled and unfashionable notions about all people being born equal and having the right to self-determination, could not immediately fill.
Into this space, as Churchill put it, "crawled the Hitlerite monster" of the fascist Nazi regime, along with other new ideologies that competed for space: anarchism, communism, and the ultimately victorious democracy. It was a time of great loss, great chaos, and great hope, and to study it is to honor the sacrifices of those who gave their lives for the victory of equality. Let's see if you were paying attention to this pivotal period.