When writing such an essay, the best thing to do is to compare the case of the two Koreas with the other major Cold War era reunification, that of East and West Germany. Since the two Germanys’ situation was very similar to that of the two Koreas, it will be useful to compare them. Germany reunified relatively successfully. If Korea is similar to Germany, it can too. If it is not that similar, it may not be able to reunify.
The main topic that needs to be addressed is how far apart the two countries have grown. The more different they are, the harder to reunify. This main topic can be broken down into a few subtopics. They include:
Duration of separation. One important thing to remember is that Germany reunified in 1990, about 45 years after it was split up. That is now 22 years in the past, which means that the two Koreas have had that much more time to grow apart.
Economic comparison. One of the most important things to think about is whether the two countries can afford to reunify. When Germany reunified, the East was far behind the West economically and needed a great deal of help. You will need to look at how different North and South Korea are economically and compare that to East and West Germany. You might look at GDP per capita levels as well as at the relative populations of the countries.
Social and political comparison. As of right now, it has been almost 70 years since the Koreas were split. If they have grown too far apart in terms of their social and political attitudes, it may be very difficult to bring them back together. You will need to address this issue as much as possible. It will be hard to find out about what average North Koreans think. But you can find compare South Korean attitudes on reunification to West German ones. You can also compare North Korean official statements and actions with those of East Germany.
By making these comparisons, you can come to some conclusions about the possibility and feasibility of Korean unification.