From a recent article in New Scientist:
Overconfident people are more likely to wage war but fare worse in the ensuing battles, a new study suggests. The research on how people approach a computer war game backs up a theory that “positive illusions” may contribute to costly conflicts.... then:
Those who launched unprovoked attacks also exhibited more narcissism, scoring 13 out of 15 on a standard psychological test. More peaceful types scored 11 on average on the same test. The trend applied to both men and women. “So it's not maleness per se but narcissism that makes some people overly optimistic and aggressive,” suggests Bertram Malle at the University of Oregon in Eugene, US.... and:
Malle agrees that the study raises worrying questions about real-world political leaders. "Perhaps most disconcerting is that today's leaders are above-average in narcissism,” he notes, referring to an analysis of 377 leaders published in King of the Mountain: The nature of political leadership by Arnold Ludwig.