Identify four physical features that form the boundaries of north and south korea

I have only three features and the major one I've put in the beginning.
Do hope you will find it helpful.

The most famous official border is placed between North and South Korea and is called Korean Demilitarized Zone. This structure is considered a warzone after Korean War that ended with signing an armistice by the both sides.

The other physical feature can be a border that appeared due to Russian and American agreement after WW2 in 1945 to grab Korea as Japan was destroyed by war. Communists installed a leader in North Korea and USA in ots turn installed a leader in South Korea which created a border.

The next and the last boundary I can describe for you occured after elections in the South Korea in May 1948. The Republic of Korea was proclaimed in Seoul in August. And what about North Korea, in this area the ideas that were proclaimed turned out completely different - the Democratic People's Republic, September. 

Ithink it is space that makes up 70 percent