Trade routes spanned Eurasia before we invented writing. Faster transportation and communication only expanded economic ties. Transportation is something that is fairly easy to do without fossil fuels.
Again, you conveniently forget the important part. Before we invented writing, we were not remotely transporting as much stuff as we are today.
I mean, before fossil fuels, the world ran on renewables. But that's not at all a proof that we can easily go back to renewables: it was a different world then.
