Ohara was an island located in West Blue. The island consisted primarily of archaeologists. Ohara came to be for over 5000 years ago, when the Tree of Knowledge was planted on the very island. For millenniums, scholars and archaeologists thrived there, learning about history, a course of action that the World Government permitted. However, 5000 years after the founding of the island, the government discovered that the scholars were studying the forbidden Poneglyphs, and ordered the island's destruction via the Buster Call. Although, the destruction was order, it was later stop by a World Noble for unknown reasons, the most likely reason is too prevent the lost of such precious information. It remains a mystery on how the World Noble was able to cease the call of a buster call if it happen, but those days are in the past now.
Today Ohara is under strict watch and control of the Marines. The once small Island has been expanded to house an entire marine base there. The 101st Marine Division whose primary purpose is to keep any threats of the World Government from getting their hands on information contain in Ohara. If you have an occupation in the Scavenger Field, then this is one place you can't past with out at least making one stop.