Imu wiping out Lulusia reminded me of what happened to the God Valley that was mentioned to have vanished without a trace
And we know that the purpose of the battle from the government side was to protect the Celestial Dragons
With Xebec having the ambition to become King of the World(Imu's current title), broke too many taboos that the government wanted to hide
So i wonder if one of those taboos was the fact that Xebec probably knew Imu's existence and wanted to overthrow him
And Imu seeing Xebec as a threat, with all the secrets he discovered decided to wipe out Xebec and god valley's entire existence
It also explains why Blackbeard(who is among Imu's targets) is seen as a threat by Imu
The Xebec plot suddenly got much more interesting after this chapter