Ohara Incident

The Ohara Incident is the event the took place in 1502 AOS 20 years ago. It was first mentioned in chapter 345 by Iceburg. In chapter 359, Robin told him that he doesn't know anything about it. This event was recorded from chapter 391-396.

This event took place in Ohara in the West Blue. This is where Nico Robin was born and lived for 8 years. This event explains who Robin is.

Origin
At the end of the Void Century, the World Government outlawed the research of Poneglyph. Because of this, countless people who tried to study the 100 missing years were killed.

Ohara was one of the Archaeologist clans who believed that they managed to evade the World Government's eyes, yet in reality the World Government always observed this island.

In 1496 AOS six people along with Nico Olvia, Robin's mother, went on a journey to complete her late husband's work. However, by the end of the six year mission, Nico Olvia and her group were caught by the Marines. Six of Olvia's people were killed while defending her and Olvia was left alive. Interestingly, Aokiji would later use this situation to lie to the Straw Hat Pirates about Robin.

The Marines managed to look at the IDs of the dead Oharans and found out that they were from Ohara. Because of this, the World Government decided that they would have to destroy Ohara.