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.
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