Void Century

Also referred to as the Blank Century, this is the period 800 years ago when a great civilization dominated the world and then at the end of the century they disappeared. At the end of the century the World Government came to power and censored everything that happened in the previous 100 years.

This period became known as the blank century because there is nothing left to acknowledge anything that happened, aside from the Poneglyphs which are written in a language that few know how to read. However, it causes a problem with the known histories of the world as nothing ties up because of that missing period, although most people do not seem to know about this information. For example Nefertari Cobra after told by Nico Robin about this missing period was completely shocked by its existence and didn't know there were parts of the world history that didn't tie in.

For the World Government, the events of this period are better left unknown as information linked to it is considered far too dangerous.

The years of this void century rages from 700-800 in the Age of the Sea

The void century was hinted during the Skypiea Arc, the numbers of date was found in Robin's flashback

The Great War
According to the Shandian chief in Skypiea, there ancestors known as the Shandorians people fought with the enemies who were out to seek the stone(the phoneglyph) over 800 years ago.

In the age of the sea, 402; the city of gold Shandora propers.

Ancient Weapons
The world government lied to the public that the reason to forbid the phoneglyph was the fear of revival of the Ancient Weapons. The ancient weapons are the superweapon may have been used for the war during the Void Century but as of now is not yet confirmed. Olny 2 weapons are metioned but was never shown. The Ancient Weapons known in the story so far is Pulton and Posidon

Ancient Kingdom
The real reason why the World Government banned Phonegyph research, it's the Ancient Kingdom the World Govenment is afried of, they are afried of it's ideals. It held great power, untie the Alliances which soon become the World Government fought against the kingdom. Knowing they will be defeated, the kingdom curved the Ancient Langauges on the stones. All records of the kingdom was destoryed, yet the name of the kingdom exicted on the stones

Birth of the World Goverment
In 800, at the end of the Void Century, the World Government was born, the took political control of the world