Twenty Kingdoms

Clover: They seem to have held great power once, but the information about this kingdom has been carefully erased. As they knew of their imminent defeat by the alliance that would later be called the World Government, they carved the truth into stone, to give to the future. Those are the Poneglyphs that still exist today...!!!

Pappug: Because they have the blood of the Creators in their veins...... Eight hundred years ago, a group of twenty Kings... ...formed a mighty organization known as the World Government.

The Twenty Kingdoms, also known as the Ancient Alliance, are the twenty kingdoms their the twenty kings combined to become an alliance that later became the World Government. During the Void Century they fought against the Ancient Kingdom, and by 800 A.O.S the Alliance became the World Government. The World Nobles are descended from these kings.

First mentioned by Clover as the "enemy" of the Ancient Kingdom or simply an Ancient Alliance, they were fully explained later by Pappug. Why or how the Twenty Kingdoms overthrew the Ancient Kingdom is a mystery.