History shows that wars are divided into two kinds, just and unjust. All wars that are progressive are just, and all wars that impede progress are unjust. We Communists oppose all unjust wars that impede progress, but we do not oppose progressive, just wars. Not only do we Communists not oppose just wars; we actively participate in them. As for unjust wars, World War I is an instance in which both sides fought for imperialist interests; therefore, the Communists of the whole world firmly opposed that war. The way to oppose a war of this kind is to do everything possible to prevent it before it breaks out and, once it breaks out, to oppose war with war, to oppose unjust war with just war, whenever possible. Mao
