The premise is a low-tech world such as Earth prior to 1600 CE but with a fixed number of magical/technological teleportation portal pairs scattered across the world. Each portal only takes travelers to its paired portal. The workings of the teleportation are no longer known so the portals just stand there and do their thing.
The question is how do I arrange for the world around the portals to not globalize? My current thought is for them to be controlled and their use regulated by what passes for local government but that is prone to change as power struggles cause them to change hands over the decades/centuries. So I am looking for something more structural to make them usable but without causing cultural/economic globalization.
My intention was that the portals would be seeded during world building and then be unmovable by means that the various civilizations have available. So they are like rivers, useful but you take them where they are.
The sense in which I meant globalization is a process where cultural and material exchange is below a threshold where it becomes more reasonable to talk of a single large civilization/economy rather than several smaller civilizations/economies with some interactions. There is no hard and fast line between these extremes but I am looking for something that helps the civilizations remain distinct rather than pushes them to merge.