Id argue that the reasons are not cultural as much as it was simple economics. Do note Germany had access to the potato, which is an incredibly productive food crop that helps guarantee food security and supports larger populations. Just like civ, a state's strength is built around their food...
I think some sort of external threat against the entire Human race is necessary for all of Earth to unify against, which in turn spurs the development of a collective "Human" identity. Maybe a plague ala Spanish flu that threatens to destroy the world, or genocidal aliens, or whatever. Humans...