Cambridge historian David Reynolds' most recent book does a remarkable job of explaining why people should know more about the first world war - and why it is so difficult to fully grasp its legacy.
Reynolds documents the conflict's profound impact on world powers as well as on embryonic nations, politics, warfare, the world economy, culture and literature.
The war prompted Sigmund Freud to "rethink his theory of the self", postulating a "drive to destroy" in addition to a drive to procreate.
At its conclusion, US president Woodrow Wilson's idealistic dream of making the world safe for democracy fell short, although millions of men - and women - around the world were granted the right to vote after the war.
"Great dynastic empires" collapsed - tsarist Russia, monarchies in Germany and Austria-Hungary, and the Ottoman empire in the Middle East, North Africa and the Balkans.
But the war also "accelerated the emergence of imperial rivals in the Pacific: Japan and the United States," Reynolds writes.
"In each case empire and race were tightly entangled, Japan being the only non-white great power while America, intensely racist itself, prided itself on not being a colonial empire."
Fascism and communism, two of the world's most virulent political ideologies, expanded with a vengeance in the aftermath. So, too, did democracy. When the war began, Europe had three republics. After the war there were 13.
Reynolds delves deeply into the British experience. Unlike allies whose territory was invaded, Britain entered the war "to defend the principles of freedom and civilisation". While other empires collapsed, the British acquired pieces of the old Ottoman empire and former German colonies, and ended up with more territory after the war than before.
But Britain's troubled relationship with Ireland would be redefined during the war years and afterward. The legacies of that would "sour the rest of the 20th century".
Some legacies haunt today's headlines. Reynolds describes the Baltic states and Ukraine as "blood lands" where ethnic conflict, political brutalisation and paramilitary violence have been "especially ferocious".
At times, The Long Shadow is almost a psychoanalysis of a world that was profoundly changed by a collective and horrific trauma. But that is no criticism. The book challenges readers to think.