There was no Target Oil, or Wall Oil. There also was never any ginormous hypothetical foreign oil company. Like, if a middle eastern company existed back then that called itself Ali Baba's 40 Oils. It wouldn't have been a monopoly.
That's the problem today. People want politicians to act against Amazon based on laws that are over a hundred years old. We never conceived of a situation where a company could have enormously powerful competitors, like Target, Walmart, and Alibaba, while simultaneously controlling an enormous market. Our laws never conceived that as a possibility.
Or maybe our laws don't really see that situation as a problem?
But whatever the case, if we want change, we're really going to need to rethink some of the laws on the books. They're going to need to change.
The laws on the books are fine. The problem is that the USDoJ and Fed courts have been captured, and don't enforce the laws as written. Judges and prosecutors invented their own modifications to the laws.
By the law as written, anybody seen exercising monopoly power is, and has chosen to be, a monopoly, and is governed by public utility rules, not regular market rules. The way the DoJ has chosen to re-interpret the law, it doesn't kick in until "consumers" see high prices. Charging below-cost prices and driving everyone out of business first, so there is after no one to compare prices to, gets no attention.
Standard Oil peak at 91% of US market for refined Oil products after 40 years, so there were competitors. Obviously there were far more competitors internationally and their international market share was far lower.
Target and Walmart are not platforms. Amazon isn't the only company selling consumer goods in general (for now), but they are the only online-seller platform in their category. Shopify exists, and Ebay exists, etc., but people wouldn't put up with stuff like in the OP if those platforms served their needs.
Trust means something fairly specific legally. A group of businesses that team up to, in theory, monopolize a market is a trust. A cartel would be when those businesses are all the manufacturers or suppliers, leaving, for instance, retailers with no other recourse but to pay the higher prices that the cartel sets.
I think what you're thinking of with Amazon is more of a monopoly. I'm not sure they really need to team up with other businesses.
EDIT: Yes. I know that Amazon does not fit the legal definition of "monopoly". I was only saying that if we bend the legal definition of "monopoly" a bit in just the right manner, Amazon would fit. Whereas Amazon would never fit the legal definition of "cartel", or "trust".
They are certainly trying to vertically integrate all of their businesses. Prime video is hosted by AWS. Amazon is getting into the delivery business. Won't be surprised if Amazon buys a few cheap factories overseas after real estate crashes, or a container vessel.