The Onion Trade History is colourful and a popular topic. I will NOT regurgitate here what has already been written elsewhere about the topic. And - I will be happily providing you with links to the quality contributions I have identified in my research.
What I will do though, is to comment on onions and their trade history from a Meta perspective...
Onions are not the sexiest of products but from a history point of view, they are certainly more colourful than their plain brown or purple skins suggest.
Onions are perishable, like any other vegetable, but can under the right conditions be stored. This means that onion prices are not quite as volatile on a week to week basis as other, more perishable, produce.
The flipside of this situation is that traders are able to gain a reasonable good overview of available onion volumes in any given season and that pricing is more likely to contain a speculative element than the pricing of other produce. Until 1958 onions were a tradeable commodity on the Chicago Commodities Exchange. Growers successfully lobbied the US Congress to pass the Onion Futures Act which banned the trading of onion futures.
On the other side of the Atlantic, the French are often the first country one thinks of when one thinks about onion trading. It is actually the Dutch who dominate todays onion trade.
Nevertheless, older folks in southern England still have fond memories of the 'Onion Johnnies', French onion sellers who would come across the Channel on their bicycles, selling onions from door door directly to consumers, before the emergence of supermarkets as one stop produce shops.
Egyptians, Greeks and Roman all knew and used onions which makes the Onion Trade History a particularly rich one. The onion was thought to have aphrodisical effects in Egypt. In Greece onion juice was used on athletes in the same way as we use body oils to keep our skin subtle and the Romans ate onions alright - but considered them to be food for the poor.
Regardless of the reason for consumption, the Onion Trade History is closely intertwined with the development of mankind.
And in India, for example, onions can impact election results!