The year was 1917 and the U.S. had just joined the ferocious fighting of World War 1. Young men, even some under the age of 18, were recruited to fight the war.
All of the combatants on both sides of the war were young men remarkably like one another and they were all directed to if need be, die for the cause. Millions of them were killed.
Following many years of seemingly endless wars, the perpetrators of those wars sat down together to establish a new set of ground rules that would make those wars less randomly lethal to civilians and to end the destruction of property, which all the leaders agreed was very costly.