"Millions of the mouthless dead"
What was really different about the First World War is just that. It was a war fought on a world scale, with bigger armies and more casualties. The casualties were much higher than in other wars because the generals were fighting the war with twentieth-century defensive weapons while using nineteenth-century attacking ideas. The real change was in the way every aspect of life at home was affected by the war, as Britain first tried to persuade men and women to support the war and ended up forcing men to fight.
Neil Demarco: Britain and the Great War; Oxford University Press, 1992/2000, page 23