This is an odd tangent, though, if you are interested in humanity's ability to do fine metalworking etc. and how this influenced what transport technologies were viable in what year. This isn't about rural backwaters, anywhere. It's reasonable to define mass adoption to mean that millions are using the thing, although obviously the first million will be in advanced bits of the world.
This is an odd tangent, though, if you are interested in humanity's ability to do fine metalworking etc. and how this influenced what transport technologies were viable in what year. This isn't about rural backwaters, anywhere. It's reasonable to define mass adoption to mean that millions are using the thing, although obviously the first million will be in advanced bits of the world.