Here is a summary of my research - and findings - on this important question.

First, I restrict this question to government murder--democide--whatever the reason, whether genocide, politicide, massacre, atrocities, assassination, ethnic cleansing, death squads, or nonjudicial executions. Second, I include all cases of such democide, no matter the number murdered, during the years 1900-1987. Third, I cover all nation-states, but look at the distinct political governments (regimes) governing each. This would then give us a total of 141 governments which have together murdered about 170,000,000 people, including near 39,000,000 in genocide, during these 88 years. Finally, if we are also to do a scientific analysis of these democides, we need a comparison group of governments that have committed no democide and that reflect the religious, cultural, racial, economic, political, and regional variation among nations. To do this I included an additional 73 governments, giving 214 governments in total to be analyzed.

Statistical analysis of these 214 governments that did or did not commit democide, including using controls, holding variables constant, etc., (through multiple regression, factor analysis, canonical analysis, contingency analysis, and analysis of variance) showed that:

• Religion, ethnicity, race, culture, wealth, education, literacy, population, area, and region has little correlation with democide. That is, one cannot explain why governments murder people by knowing any of these characteristics of either the leaders/rulers of a government, or the nation itself.
• The only characteristic that generally predicts to (is highly correlated with) democide is the degree of unrestrained power of a government. That is, the less liberally democratic a government, the more likely it will murder its people and foreigners under its control. The worst demociders are those governments giving their people the least freedom; the least demociders are those governments most democratic.

This gives us a political structural answer to why governments commit democide. They have the power to do so.

But then, why do they use their power to so kill? I've done a large number of published case studies on this, and there are several reasons, often mixed for specific democides.

• Getting power - specifically the achievement, winning, or assumption of unrestrained power by those with a utopian, theological, revolutionary, or reconstructive ideology (fascism, communism, state socialism as in Burma, Islamism as in Iran).
• Responding to an actual or potential threat to the power of a government (Pakistan re East Pakistan, Sri Lanka, Rwanda, Burundi, both Congos, Liberia, Sudan, etc.).
• Consolidating government power (Afghan's Taliban, Iran, Post WWI turkey, colonial democide).
• Opportunity. When there is war/revolution/conflict this can be an excuse to implement desired/promised ethnic/religious/political goals, such as "ethnic cleansing"(Holocaust, Armenians, Gypsies, Kurds, Shiites in Iraq, Serbs in-WWII Croatia, Kosovo Moslems, post-WWII ethnic Germans in Eastern Europe).
• War. War so totally involves government, with a ready excuse for few restrictions, that it can use democide as a strategy and tactic, as was done in revolutionary Mexico, in WWII by the United States' A-bombs and firebombing, Britain's urban bombing, the Soviet's lethal relocation of minorities, Nazi Germany, Imperial Japan, both Nationalist and Communist China, and is currently being done by Russia in Chechnya, the terrorists/insurrectionists in Iraq, and the Palestinian Authority against Israel.
• As an instrument of control over the population, such as in current China, Vietnam, Laos, North Korea, Iran, Syria, Burma, Cuba, and Saudi Arabia.
• As a method of maintaining power (all totalitarian countries, at least).

If this is all true, what about the many alternative explanations, such as economics (notably Marxism), social psychology (racial hatred or ingroup vs outgroup), and human psychology (a leader's awful youth)? These have a secondary role, if any, and are specific to those ruling governments that have the power to commit democide. These factors may moderate or enhance democide, but do not change the fundamental dynamics. Regardless of the psychology or ideology of the leaders of a democratically free nation, they are exceedingly unlikely to commit democide-not because they are flawless or better people, but they don't have the power to do so and get away with it.

To be sure, the agents or officers of democratic governments can commit democide if operating in secret or during the pressures/excuse of war, e.g., My lai, Hiroshima, but the democratic government in general cannot). However, if the leaders are dictators or rule an authoritarian government, then an explicit threat to the power of their government, for example, usually will provoke democide regardless of who has this unrestrained power. A leader who operates in the Machiavellian world of absolute power already has a certain kind of psychology. There is a pattern here of democidal behavior by those holding such power that transcends the usual social and social-psychological categories and explanations.

What does all this mean for ridding the world of democide? Simply this: we don't have to worry about changing the psychology and personality of people so much as to prevent in the first place anyone from having unrestrained power. That is, we should concentrate our resources on promoting human rights and democratic freedom, a far easier task than trying to control or change the social-psychological characteristics of leaders/rulers.

This answer applies beyond democide to any kind of political violence, at any level. Democracies don't make war on each other, and the more democratic two nations, the less likely their military violence. Moreover, the greater the democratic freedom of a nation, the less its foreign and internal violence. So we also have an answer that goes beyond democide and provides a general answer to why governments kill even by going to war. That answer remains unrestrained power. Indeed, I put it this way:

R.J Rummel, Professor Emeritus of Political Science and Nobel Peace Prize finalist, has published twenty-nine books, and received numerous awards for his research. See his short bio.