I think that this Memorial Day Weekend it's a good idea to post a diary revisiting why this holiday was expanded to commemorate not just those who had fallen in the Civil War, but all wars. It's about the Industrial Revolution, the evolution of modern warfare, the rise of international movements, the failure of them at the expense of nationalism and isolationism, and the lessons for us.
About WWI Dyer writes:
All the European armies had professional general staffs long before 1914, and they devoted their time to making elaborate plans on how the next war should be fought. (Indeed, their plans were a major factor in making it more likely that war would come.) They understood the effects of new weapons like the machine gun, which had seen use in small wars and "colonial wars." Even civilians like Hilaire Belloc knew that European troops would always beat the natives because
Whatever happens we have got
the Maxim gun and they have not.
But the generals had not done the crucial calculation, which was to multiply the width of the front that an individual infantryman could hold by the millions of men who would be available in a European War. The answer of course was that the armies could spread out to fill all space in a continuous front.
And so they did...
Dyer's book is especially cogent in its description of WWI, but to appease the copyright gods, let me summarize.
The net result of this method of war was the application of the modern industrial revolution in a perverse, reverse kind of way, where mass destruction of material, men, horses, farms, and land was carried out at horrendous rates.
Years' worth of production of shells were being consumed in battles that lasted days in which of the order of a million people were killed in that one battle alone.
The US entered this war (after Mexico was encouraged by Germany to become a belligerent against us), and when our tanks and troops arrived and fought, Germany and the other Central Powers eventually collapsed. (Some of our troops were armed with shotguns, which was viewed every bit as much as a war crime as the use of poison gas in some other times and places. You see, you didn't need to aim when using a shotgun, and they were quite effective at relatively close ranges.)
After all the slaughter - it was at its time the most horrific slaughter Europe had ever known with about 15 million killed, and affected Brittish birth rates for the next generation- it was only fitting that Memorial Day, originally commemorating America's worst military slaughter, would be extended.
For more about WWI, Here is an excellent source.