The Crystal Alliance is the name given to the group of planets ruled over by the Next Gen Crystal Gems in the future.
The Crystal Alliance was formed after the 3rd War, each gem colony divided among the main 9 members of the Next Gen Crystal Gems. It is currently peaceful and had found ways of artificially implanting gems into the children of half gems if they wish to have them, though it is compulsory in the noble and royal families for children to become half gems. Though many of the planets have a similar history of being gem-colonies, the moon was quite different.
It was a peaceful gem civilization with history going back predating the diamonds' conquest. Founded by Queen Celenia (Celenia the Light), it interacted with earth the gems on the moon procreated with humans and for a while the Kingdom was bountiful with wealth and peace until the diamonds drew close. Years rolled by Queens Yue (Yue the Lonely), Artemis (Artemis of the Arrow), Crescent (Crescent the Glorious), Chaandanee (Chandanee the Goddess), Maanblom (Maanblom the Fairest) Bulan (Bulan the Avatar), Yoru (Yoru the Enchantress) and Silver (Silver of the Spindle) held back many adversaries from Homeworld. Until the reign of Queen Shadow (Shadow the Traitor) whom sold her own Kingdom to the diamonds, for a Sunstone that wooed her. White Diamond and Shadow attacked but were defeated by Luna's mother Queen Rainbow (Rainbow the Undefeated). Eventually the Kingdom fell and was taken over by Pink Diamond. Only to be revived 6000 years later by Luna.
Sagittarius Star Spire: Location of each monthly meeting of the Alliance leaders and birthplace of Prince Sagittarius.
Kingdom of Celenia: Otherwise known as the Moon, currently ruled by Queen Luna and King Calvin. Prince Sagittarius is the current heir to the throne alongside Princess Siren.
Principality of Ursus: A cluster of stars located in the Ursa constellation, currently ruled by Princess Kalani (Kitty) and Prince Minato, Lady Sayaka is current heiress to the throne.
Empire of Terra : Groups of Earth-like planets, currently ruled by Emperor Stephen (Steven) and Empress Connie. Princess Rose is the current heiress to the throne.
Grand Duchy of Olympia: A cluster of planets in the Orion constellation, currently ruled by Grand Duke Joseph (Joe) and Grand Duchess Ivy. Prince Scorpius is the current heir to the throne alongside Princess Libra and Princess Persephone.
Kingdom of Medea: A group of stars and planets in the Scorpius constellation, currently ruled by King Alexander (Rex) and Queen Chantal. Prince Comet is the current heir to the throne.