[Retra]

The only technology needed for this to happen was a common understanding of language. The only people you can't trade with are those you can't communicate with. And cities can issue their own currency; they just can't convince anybody to use it.

I would argue that the trade system is far less restrictive because you can easily trade globally rather than only locally. You also can't get away with pillaging/defrauding your neighbors and calling it 'trade' anymore.