What do banks do with money we deposit?

Well, the bank primarily does two things: loan the money we put into the bank, and pay interest annually to your account. The interest is basically to say: since we are loaning your money to other people, we'll pay (and this is just an example) 10% interest of what you put in your bank account.

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.

warfare was the primary means of cultural transmission in both regions.