There's more to be said, but you might like to read my response to the question It’s August 1st 1914. I’m a 20yo Parisian male who just heard Jean Jaurès was shot dead and I desperately want to avoid fighting in the Great War. Can I still flee to the UK or preferably US? When would it become harder? An 18 year old would have nothing to fear in any case. France's conscription laws only mobilized men when they turned twenty.