The Three Great Powers

As of chapter 432, the long-standing question as to the identity of The Three Great Powers has been answered. The Powers are, as identified by a Vice Admiral, the Marine Headquarters, the Shichibukai, and the Yonko or Four Emperors, which is the third and last of the Powers to be named.

These three institutions exist in a delicate balance, not much is known about how this functions. It is however known that only the other two organizations are equivalent to the Yonko. Considering that these organizations are stated to be a balance and the fact that the loss of Crocodile threatened said balance, the most reasonable conclusion is that each organization is roughly equivalent in strength.

The Gorousei fear that if this balance gets disrupted, the world itself could collapse around them. It has not yet been fully explained so far as to why one of the Three Powers being weakened could pose such a dangerous threat. One possible reason is that this stems from the fact that only the Marines are fully under the control of the World Government. The Shichibukai appear to follow orders on a whim if at all and the Yonko are entirely outside of the World Government's control. A damage in the balance could swing the scales toward the Yonko and might lead to the Shichibukai reverting to their old ways in support.

The only other thing known about the Three Powers is that they are collectively the reason why the Grand Line is called the Pirates' Grave.