Ars Magica Transforming Mythic Europe
Hermetic magic has the power to change the world. A magus fresh from apprenticeship can create a land to rule where there was nothing but ocean. Magic can replace much of the back-breaking labor typical of the medieval world. Even without changing their use of magic, magi could upend the structure of society by involving themselves in its problems and politics. But magi avoid such activities. They know the risks involved, and do nothing that might upset the status quo of Mythic Europe.
Except when they do.
This book describes the magic and activities necessary to transform Mythic Europe, whether by creating an island for magi to rule, integrating the Order of Hermes into wider society, or starting a technological revolution. None of the magic is particularly hard, nor does it rely on hidden secrets. Magi have not changed Europe because they have not yet chosen to. Your magi may choose differently.