Why we love it
It is said that 1914 saw the end of romantic war, that the nations of the world finally woke up to the horrors of combat. The century before that was the age of imperialism, where nationalism ran rampant after it was awoken by revolutionary France. Nations could do no wrong, they brought "civilization" to Africa, India, East Asia. Europe was the center of the world and nations vied amongst each other for supremacy.
The British, French, Germans, Austrians, Italians and Russians had little doubt of their own moral, social and international superiority. It was manifest destiny on a grand scale, and this pride - both among the leaders and the populace - is what led to the deadly arms races which in turn exploded into the Great War. Each side was confident of victory, wars would be short and the blood would be shed on the other side.
European experience, after all, was based mostly on the recent conflicts in Europe itself, like the Seven Weeks' War between Austria and Prussia, or the Franco-Prussian War of 1870-1871. The lessons of the Crimean War - poor leadership, underestimation of firepower and fortified positions were ignored as being outdated and part of a limited conflict. Similarly, the lessons of the American Civil War were ignored as being a "colonial" matter, a primitive war in an alien environment.
Thus, both sides entered World War I with the highest expectations of glory. Civilian populations cheered the soldiers on, the young men promising to come back to their girls in time for Christmas. Germany's Schlieffen plan commited most of its forces into a wheeling attack through Belgium down into France, forcing an early capitulation of France on the western front and then quickly transfering its forces back to the eastern front, where a minority of Germany's armies were to fight a delaying action along with the Austrians.
Of course, we all know how that turned out. Soldiers dug in to trenches, pounded by artillery and kept down by snipers and machine guns. Old guard generals, learning nothing from successive failures, relying on lessons from wars 40 years old, sent their cavalry to die futilely in between trenches, forced men at gunpoint "over the top" to get slaughtered by withering machine gun fire from enemy trenches - and then blamed their failures on morale. The romance of war was slow to fade on the home front, but no government could disguise the horrific casualties for long.
Thus, the Allies, the winners of World War I, were hesitant to fight another war. People were tired, disillusioned and terrified of another such conflict. American isolationism - difficult enough to overcome during World War I - would dominate the political scene until Pearl Harbor.