Over the past decade the liberal peace—the finding that democracy and economic interdependence contribute to peace among nations—has emerged as one of the strongest and most important results in the scientific study of international relations. Recent research indicates, however, that the pacific benefits of democracy and interdependence may not be unconditional but contingent upon the wealth of nations. We assess the independent and conditional influences of democracy, interdependence and economic development on the likelihood of fatal militarized disputes over the period 1885 to 1992. Economically important trade has an independent, substantively important pacifying effect, but the conflict-reducing effect of democracy depends on the level of economic development. If the less developed state in a dyad has a per capita GDP below 1400USD, joint democracy is not a significant force for peace. Our results indicate that the vast majority of past research on the democratic peace is imperfectly specified because the character of states' political institutions alone does not account for the likelihood of military conflict. To advance further the cause of peace, we must encourage increased global trade and development along with democratic institutions.