While some tin certainty was mined in England, its not the only supply line in the bronze age.
> You miss the point about caravans: everything they carried in any volume were things there was a known and hungry market for.
No, I am not missing the point, the argument Graeber makes is very clearly about the denial of high risk entrepreneurial discovery.
I explained there is still market risk, supply lines are not perfectly stable and the don't just magically spring up with high certainty. Supply lines grow over time, extend, mutate and so on. Its called entrepreneurial discovery and it has been well studied in economics (something that seems to have almost no function in Graeber world view).
Of course volume increases as security increases, but even then the risk is still substantial. All European to Indian Ocean trade was incredibly high risk for the interior existence.
Non of your responses undermines my central argument I would say.
Portuguese sailors absolutely had been to India. But getting through the maze of canals in Egypt to the Red Sea was more expensive than they liked.
You miss the point about caravans: everything they carried in any volume were things there was a known and hungry market for.