ELI5 Interest Rates - why do interest rates exist in the first place?

How did civilizations originally justify charging interest on money? How does raising interest rates slow/lower inflation? Do banks lose money if they lend money at less than inflation? What does the term usury mean? Why is interest banned in Islamic finance? How come people don't borrow from low-interest rate countries like Japan and deposit it in high-interest rate countries like Argentina?

... we explain like I'm five

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