Remnants are still there.
The forests around Verdun, where so many died, are still and silent.
There in front were the unmistakable features of French trenches - deep channels, virtually unchanged, that sheltered men struggling to and from the front line.
In 1917, the Canadian Corps attacked and captured German positions on the hills around Arras. More than 3,000 Canadians died. The shell holes and trenches are now covered by a manicured carpet of grass - Canada has adopted this corner of France as its own memorial. The warning signs remind visitors that unexploded shells and grenades lie where they fell.
A lot of modern Western history can be traced to World War One. It at least hastened the collapse of Czarist Russia, opening the way for the Bolsheviks. Germany was scarred by the humiliating surrender terms, which contributed to conditions that Hitler exploited. The conference that drew up those terms also rearranged the world into colonial powers, angering those who were left out (Japan) and those who were colonized (Ho Chi Minh, the Middle East). The Balkan nations are still grappling with the results.
The combination of 19th Century ideas with 20th Century technology ground down the old order and left a smoking ruin from which to establish a new one. We've been sweeping up the mess for 90 years, and we're not done.