Singer–Prebisch thesis

The Singer-Prebisch thesis says that the price of goods that are traded between countries changes over time. Basically, it says that prices of goods made in richer countries (like the US or Canada) get more expensive over time, while prices of goods made in poorer countries (like Bangladesh or Ethiopia) get cheaper over time. This means that poorer countries struggle to make money from trading, so they don't get as many benefits from trading as richer countries do.