From various news reports, it's my impression that the majority of migrants both to the USA and across Europe tend to be young, unaccompanied men ( = "of military age.") This should not be surprising when you look at the demographics of the places these invaders, pardon me, "refugees" originate. In the best of times, young unemployed men are a social problem: Remember the old saying "Idle hands are the Devil's workshop?" I'll leave the question of whether The Prince of Darkness really exists, but it's a fact that surplus population of any type is bad news, and young males are the worst. Also, from the exporting country's point of view, it's win-win to have the excess population offloaded elsewhere.