[Menes]

Sorry, but are you sure this was the case with Russia, France, Germany or Austria-Hungary, too?

I remember that conscription in Britain was not instituted until January 1916 - but other European nations had had the draft for decades before WW 1.

[Angelino97]

Well, All Quiet on the Western Front speaks of entire graduating classes rushing to enlist in Germany in 1914.

I've also seen films and documentaries saying the same about Russia. The Bolshevik in Doctor Zhivago mentions peasants rushing to enlist.

Those nations might have had standing armies. But when war broke out in 1914, they needed more men, and a great many eagerly enlisted.