"[E]very act of aggression between nations; every act of terror and corruption and cruelty and oppression that we see around the world shows our work is never done. We may not be able to eliminate man’s capacity to do evil, so nations –- and the alliances that we’ve formed -– must possess the means to defend ourselves. But among those nations like my own that hold nuclear stockpiles, we must have the courage to escape the logic of fear, and pursue a world without them."