Which countries are most likely to fight wars?

WHEN THE first world war ended on November 11th 1918, David Lloyd George, Britain’s prime minister, told Parliament: “I hope we may say that thus, this fateful morning, came to an end all wars.” History proved him wrong. But 100 years on, the world is far more peaceful. Fewer than one in 100,000 people have died in combat per year since 2000—one-sixth the rate between 1950 and 2000, and one-fiftieth of that between 1900 and 1950. Why?

The simplest explanation is the advent of nuclear weapons, which deter major powers from fighting each other. But wars have declined among non-nuclear states, too. Another reason might be the spread of democracy and global norms. Bruce Russett and John Oneal, two academics, have found that countries that are democratic, trade heavily and belong to lots of international bodies fight each other less often than authoritarian, isolationist states do.

The Economist has analysed all international and civil wars since 1900, along with the belligerents’ wealth and degree of democratisation (assigning colonies to their own category). We counted all conflicts involving national armies in which at least 100 people per year were killed, excluding deaths from terrorism, massacres of civilians outside combat, starvation or disease.

The data show a strong correlation between democracy and peace, with a few exceptions. (The United States has been quite bellicose, and its advanced democracy did not prevent a civil war in 1861 that claimed more American lives than any conflict since.) Moreover, the relationship does not seem to be linear. The countries most prone to wars appear to be neither autocracies nor full democracies, but rather countries in between. A similar finding applies to prosperity. Middle-income countries are more warlike than very poor or rich ones.

What causes such states’ belligerence? Warfare is expensive, and citizens in tyrannies struggle to organise uprisings. Some studies find that civil wars are more common after sudden regime changes, which cause instability. Perhaps a little political competition or wealth make it easier to take up arms. All this might explain why the bloodiest battles since 1900 have shifted from Europe, to Asia, to the Middle East and Africa. If partial democracy is linked to conflict, recent backsliding in countries like Turkey looks even more worrying.

Even a bit of democracy, however, saves lives overall—because empires and dictators are more likely to starve and slaughter their subjects. Counting man-made famines and genocides, colonial and undemocratic powers have caused 250m premature deaths since 1900—five times the death toll from combat in all wars combined.