The "Great Kingdom" was a kingdom said to be enormous, prosperous, and powerful. Its true name is a mystery, as the Gorosei ordered that Clover be shot before he could speak its name. It was likely an enemy of the Twenty Kingdoms (which is now the World Government), as implied by Professor Clover, and was seemingly utterly destroyed by them over eight hundred years ago at the end of the Void Century. In fact, it seems their defeat allowed the Ancient Alliance to truly become the World Government. Furthermore, it is the real reason the World Government has banned any Poneglyph related research as the mere "existence and idea of this kingdom presents a threat to the World Government".