MEH, mc is not thinking straight, he can dominate the planet within 10 years if he does it right.
The fastest way is to use the ship AI to control droids in all major cities and proyect a hologram of the "Goddess" and provide a prophecy by saying that in 1200 years, invades from the stars will come and destroy the world, then proceed to show an EDITED footage of each city in ruins with insects the size of people slaughtering everyone and showing their spaceships and all, by saying that this is the future 1000-1200 years later and that of this moment any wars between countries is forbidden and that they will be anexed with the "Empire of the goddess" and that her apostole will unify the whole world under one banner, and should anyone resist, she says with a sad smile that they will recieve my wrath as they are getting in the way to save this world.
AS a proof of this, her apostole and champion will conquer the demon forest and build "heaven" city within 5 years.
Naturally some people will revolt, but with the droid, they can be found and then eliminated.