In the New York Times, William Boyd considers why for the British 'the memories, images and stories of 1914-18 seem to have a persistence and a power that eclipse those of the Second World War'. He ventures some reasons he thinks specific to this country: in Europe, he says, the memories of the First World War were partly erased by the Second, more so than here. At the centre of his explanation, however, is the sheer scale of battlefield slaughter, which 'defies credulity':
[I]t is the Western Front and trench warfare that define the war in memory. It was a deadly war of attrition in which millions of soldiers on both sides slogged through the mud of no man's land to meet their deaths in withering blasts of machine-gun fire and artillery. And at the end of four years and with about nine million troops dead, the two opposing forces were essentially where they were when they started.
.....
... The tactics were 19th century - advance on the enemy. But the enemy had weapons of mass destruction - the battlefield was dominated by tanks, machine guns, howitzers, aircraft and poisonous gas. Some 117,000 American servicemen died in the 19 months of United States participation in World War I - more than twice as many as in Vietnam, nearly 20 times as many as in Iraq and Afghanistan.No society today would accept such a horrendous casualty count. At the beginning of the Battle of the Somme, on July 1, 1916, the British Army suffered 60,000 dead and wounded - in one day. It was arguably the worst butcher's bill in military history, of army versus army. There is a very real sense in which the modern world - our world - was born between 1914 and 1918. Something changed in human sensibility. Soldiers wouldn't be willing to engage in such slaughter. Toward the end of the First World War, even, tolerance for past norms had begun to end. In 1917, much of the French Army mutinied and refused to attack. They would defend but not attack. The days of cannon fodder were over forever as a result of that war...
It doesn't directly contradict Boyd's suggestion about the way WWI altered modern sensibilities, but I have seen it suggested more than once that, by its brutalizing effects, that war may have played its part in preparing the ground for the Nazi genocide in Europe.
