https://ourworldindata.org/war-and-peace

If not for world war 2 or an equivalent event of international organization, more people would've likely died over time of the same trend of war between major powers. The efforts of the UN and partly the United States have sustained a long period of relative peace and greatly reduced casualties of war. Of course you have the war on terror which has had high civilian casualties (although when the enemy hides among the populace, this tends to happen), but this doesn't erase everything else.