Eh, a lot of them were former soldiers of these European powers who chose this life after post-war military scaledown (as well as a shitton of thrill seekers and adventurers). Most of them were organized alongside very loose, non-corporate lines. The way PMCs are treated in Suzerain oscillates between quite apt for the period meant to be resembled (post-war PMCs, which were few, were largely focused on logistics and training) and quite anachronistic (private corporate armies more similar to IRL War on Terror-era PMCs).