The United States already has a draft. All citizens must sign up for it when they turn 18. While it has not been used probably since Vietnam it still could be put into effect at any time. It is only necessary if we end up in a war with a major power and loose a bunch of troops. Any imitate conflict even one with Russia likely would not require it.
You better hope it's a virtual war, Cause these kids don't know how to do anything other than play video games. Ender's Game? Yeah - they'll beat the aliens. Apocalypse Now? Hell no - they don't know how to work rotary dial phones. Clash of Turbans? Maybe - is it first person or scrolling?
I think we would see something like the great depression and maybe that's why we don't right now but if we did there would be not as many workers which mean not as many buyer and sellers which would bring us what I think another great depression so I think we shouldent