It's not just WW1, it's that the system or rules the society is organized in has changed. Under feudalism, one of its basic tenets was that vassals provided their liege with not only money, but certain amount of men for the army. Hence the "For everybody involved, it was a duty and a question of honor." part of the quote. Although I suspect that for common peasants, there was no sense of duty or honor in this, it was just a potentially family-destroying event, where men would be rounded up and marched off against their will to die.

Modern society sometimes still has that in limited form (mandatory military service), but it's very different, and time-limited.