I don't see what it has to do with anything, but King Manfred tried to begin large-scale campaigns to claim territory and spur economic growth in light of trade routes shifting to the high seas, denying Ala Mhigo one of its main sources of income. Gridania caught wind of this and deployed troops to the Velodyna River; the rest is history.
What life would have been like under an Eorzea ruled by Ala Mhigo is both unknown and unknowable. It's kind of a moot point.