Hello.
The main reason was because They had to pay higher prices.
Monopolies meant the violation of competition laws and prices were higher since competition was squeezed out. Farmers in the Midwest had to pay higher prices because of the monopolies in the railway sector to send and sell their crops to the East. They opposed it and joined the Populist movement.Monopoly is a market structure defined by a single seller, selling a unique product in the market.
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