The First World War inaugurated the manufacture of mass deaths that the Second brought to a pitiless consummation. - John Keegan

The basic and stark fact, nevertheless, was that the conditions of warfare between 1914 and 1918 predisposed towards slaughter and that only an entirely different technology, one not available until a generation later, could have averted such an outcome.
The first day of the battle of the Somme, 1 July 1916, was to be an awful demonstration of that truth.

Within fifteen years of the war’s end, totalitarianism, a new word for a system that rejected the liberalism and constitutionalism which had inspired European politics since the eclipse of monarchy in 1789, was almost everywhere on the rise. Totalitarianism was the political continuation of war by other means.

Plans made without allowance for the intentions of the enemy are liable to miscarry. So it was to prove in 1916.