According to wikipedia, the only countries that use the MM/DD/YYYY system are the US, the Philippines, Palau, Canada, and Micronesia.

Does Korea use mm-dd-yyyy?

The national standard (KSXISO8601, formerly KSX1511) also recognizes the ISO-8601-compliant date/time format of YYYY-MM-DD HH:MM:SS, which is widely used in computing and on the Korean internet.

How do you write dates in different countries?

And in fact it is, ISO 8601 sets the international standard for writing dates as YYYY-MM-DD. However, as the map above shows, that format is not commonly used outside of East Asia. Instead you have all sorts of different formats being used. The most common is the exact opposite of ISO 8601 and goes Day-Month-Year.