Let's say we are facing each other in a wild where there isn't any nation, rule, and law. Assuming that we both have weapons on our hands, what do you think would going to happen? 
Nation is the largest community to ensure an individual's rights. Yes we do have the United Nations and international law, but that isn't a nation of nations. UN weren't even able to send multinational force when the North Korea invaded the South Korea, if the Soviet Union vetoed the agenda for sending troops. 
So the relationship between nations is like the relationship between men in the wild. What would happen if I just drop my weapon believing that you won't threat me with all the advantages? Even if you would not murder me, it is so easy for you to bully me and take advantage of me. 
Men in the wild can form a huge society only if they share same value or have something in common and there must be greater benefit if they unite. That could be a religion or blood or ideology. The relationship between South Korea and North Korea has gone way too wrong once the North Korea invaded us with hundreds of Soviet tanks. They deny South Korea, we deny North Korea. Our ideologies are very different. For us, reunion with the North Korea means a severe economic crisis, and it means the fall of the ruling circle for them.
 So the only choice left for us is 'Para Bellum'. We have to draw a line, and we should make sure that the North Korea don't cross the line even an inch. When the North Korea can't cross the line even an inch, our freedom is guaranteed. That is the way of attaining the freedom, and there is no another way around.