Why are democracies unusually successful in war? We find that superior human capital, harmonious civil-military relations, and Western cultural background are largely responsible. These traits correlate positively with democracy, and account for democracy's apparent effectiveness bonus. This is either good news or bad news for democratic effectiveness theorists. Many believe that democracy causes these traits. If so, our findings strengthen democratic effectiveness theory by explicating its causal mechanism. But others see democracy as a consequence rather than a cause of such traits. If so, our findings challenge the thesis by identifying alternative causes of the effectiveness bonus previously attributed to democracy. Either way, the results show a powerful effect for unit level variables in military performance. In the process, these same results sharpen our understanding of military effectiveness in general, and the relationship between military performance and regime type in particular.
