The Silver Millennium refers to a peaceful era in the fictional universe of Sailor Moon, lasting for a thousand years. During this time, the Moon Kingdom flourished under the rule of Queen Serenity, who governed with wisdom and compassion. The kingdom was home to the Sailor Guardians, a group of powerful warriors dedicated to protecting the universe from evil forces. This era came to an end when the dark entity known as Queen Beryl attacked, leading to the fall of the Moon Kingdom. The conflict resulted in the tragic loss of many lives, including the Sailor Guardians, and marked the beginning of a new cycle of rebirth and struggle for peace in the universe.