Korean currency
In 1902, won was introduced as the official currency unit replacing yang at 1 won = 5 yang. The bank of Korea was established 1909 but soon after in 1910, Imperial Japan annexed Korean Empire. Under Colonial rule, the country was made to use the currency unit "yen" in the name of Korean yen, which took over the Korean won at par. After the division of Korea, the state of South Korea was established and recognized in 1948, and won was again made the official currency of the new state. "jeon" was made the subunit of the currency that divided it into 100 equal parts. Bank of Joseon issued the currency for independent South Korea for the first time that too in banknotes only.
Convertibility
Some countries pass laws restricting the legal exchange rates of their currencies or requiring permits to exchange more than a certain amount. Some currencies, such as the North Korean won, the Transnistrian ruble, and the Cuban national peso, are officially nonconvertible and can only be exchanged on the black market. If an official exchange rate is set, its value on the black market is often lower.