The technical term for megalomania is Narcissistic Personality Disorder. The problem here is that virtually no one with this mental illness is aware of having it. Part of the syndrome is that you think you're perfect-- mentally as well as physically. So we can't just wait for the individual in question to admit to the illness. It must be diagnosed, like any other disease, based on whether the symptoms are present. Anyone with more than half the following symptoms can be diagnosed with NPD:
1) grandiose sense of self-importance 2) preoccupied with fantasies of success, power, brilliance, beauty, etc. 3) believes that he or she is "special" and cannot be understood except by other "special" people 4) requires excessive admiration 5) believes other people should automatically comply with his or her expectations 6) interpersonally exploitative 7) no empathy 8) often envious of others or believes others are envious of him/her 9) arrogant, haughty
Perhaps a case could be made that Kim Il Sung had at least five of these traits. It's easier to fling an unscientific term like "megalomaniac" at someone than to do the real work of assessing the case for Narcissistic PD.
What's really interesting is the prevalence of narcissism in groups-- tribes, schools, sports teams, corporations, countries, etc.-- rather than merely individuals. Amazingly, all nine of these traits apply *perfectly* to the United States in its relations with other countries. (Replace "people" with "nations" and "interpersonally" with "internationally.") The question is not so much whether the leader of a country is disturbed but if the country as a whole is disturbed. In our case, this means that otherwise normal Americans are pathologically narcissistic when it comes to US. To overcome this condition, it's necessary to cease identifying with the US. It's an ego thing.
Ted