The reason why we need a system of currency exchange in order to conduct international trade is because different countries use different types of currency. They do so because national sovereignty allows each nation to establish its own currency. However, we need a system to pay for goods that are purchased from other countries. This is why the currency exchange system allows us to conduct international trade
Japan is a island country, or in other words an archipelago. Hence, it was hard for other imperial countries to invade Japan. Japan also isolated itself from the rest of civilization.
