One Piece Episode 531

[DarthEnderX]

Then why haven't the Emperors destroyed the WG if they are so mighty?

Because they are enemies of each other as much as they are of the WG, and taking on the WG would weaken them to the point where one of the other Emperor's would take them out.

Then why haven't the Emperors destroyed the WG if they are so mighty? Because they aren't. They are pirates. Criminals, that is. The only reason why Whitebeard could pull off the attack was Ace. And even then he got backstabbed by one of his own men. The threat of a horrible retaliation indeed would be very real, but by no means assured. Even if an Emperor in name commands lots of men, ships, and power, it's not like the true military of WG, it's just a bunch of pirates whose own pockets will always be closer than the common good - unless you really get them thrilled like by saving Ace (and are a fricking Whitebeard who could turn a regular forest into an army of ents to follow him by sheer inspiration).

The quality of the troops is kind of irrelevant when they guy in charge can simply sink your island if you piss him off.

Again, if the WG had destroyed Fishman Island, Whitebeard could have simply sunk Marineford at will. The implication is that the other Emperors, which not as strong, are similarly strong. The makeup of their crew being full of backstabbing pirates is fairly irrelevant one the INDIVIDUAL PERSON is capable of inflicting catastrophic reprisals all on his own. It's the only reason the Ace trap worked, because Whitebeard couldn't destroy the island without killing Ace.

But still, this has got absolutely nothing to do with what I was saying originally: That the Fishman island goverment seems weak and the rebels are at least partially justified in wanting a strong one. Even pirates have three strong "nations", so it's a disgrace the fishmen and mermen don't.

Yes, individual kingdoms are weak. This is not a new concept in OP. See: Alabasta.

It should be obvious by now that "people" don't matter in OP. An organization is as powerful as it's strongest member. Neptune's Army only needs a couple huge badasses to be able to repel threats from the outside.