Megalomania is an unrealistic belief in one's superiority, grandiose abilities, and even omnipotence. It is characterized by a need for total power and control over others, and is marked by a lack of empathy for anything that is perceived as not feeding the self.
Although megalomania is a term often ascribed to anyone who is power-hungry, the clinical definition is that of a mental illness associated with narcissistic personality disorder (NPD).
Narcissism is most simply defined as self-love. Though it is considered healthy to care about your own well-being and have a healthy self-esteem, when someone loves himself to the exclusion of all else and others become objectified to be used only to serve the self, this is no longer considered healthy or normal.
There are different psychological theories about how and why NPD develops, most of which relate to the integration of different aspects of ego and self as a child, and the nature of the parental roles in that process. Regardless of theory, NPD is characterized by extremely low self-esteem, which is compensated for by delusions of grandeur and megalomania, a narcissistic neuroses. With the propensity to act only on behalf of one's self, the unbridled need to feed one's ego, and the objectification of others to serve the power-hungry needs of megalomania, it is easy to see how this can be a recipe for disaster, especially when wrapped in a charismatic personality.
One of the most well known examples of megalomania in modern history was Adolf Hitler. A street waif, Hitler wasn't content rising through the ranks to become the military leader of Germany. His megalomania drove him to aspire to conquer the entire world. Being born into a "superior race" also wasn't enough for the mentally ill Hitler. Instead, he wanted to wipe out all other races. This need to destroy everything outside of what he perceived as an extension of himself is a classic though horrifically illustrated example of megalomania. Paradoxically, a person who exhibits such tremendous ego and self-confidence in reality has such low self-esteem and such a fragile ego that he cannot abide any expression other than his own, for fear of annihilation of the self. Therefore everything that is not under his control is perceived as a threat.
While genocide is an extreme example, serial killers may also suffer from megalomania. They objectify, then sacrifice their victims to exercise total control with a complete lack of empathy for the suffering of others.
The principles or characteristics of NPD and megalomania can also be expressed in lesser degrees or in a different fashion by those we might consider more mainstream than genocidal maniacs and serial killers. Among dictators, fundamentalists, and politicians we find those who view themselves as morally superior with the willingness to sacrifice, kill, or risk the safety of others considered inferior in order to assert their own agendas. Though there are legitimate circumstances in which leaders must exercise civil or military force, or religious zealots can profess solemn beliefs, the line between religiosity and fanaticism, between duty and megalomania, can be a gray one. This is how the term has become part of our culture's vernacular.
Megalomania is also sometimes associated with bipolar disorder; a depressive illness that is characterized by mood swings from extreme lows to extreme highs. During the latter cycle, people often suffer delusions of grandeur and feelings of infinite capability. They talk about unrealistic plans and goals as if these plans and goals are within their grasp.
NPD, megalomania, bipolar disorder, and schizophrenia can all be treated with medications. If you or someone you know is experiencing manic moods, unrealistic delusions or antisocial behavior, professional treatment is necessary. Unlike a virus or cold, these disorders will not improve without treatment.