Mazandaran (2013)

From publisher blurb:

Mazandaran!

Mazandaran is most famous for its World River, a single river that cuts a channel almost the entire circumference of the planet. The river forms the heart of Mazandaran society, it is the life-blood of the economy and a single ribbon of settlement wrapping itself around the world.

Society is civilised, law-abiding and peaceful. Once disparate tribes governed separate stretches of the river, but unification was followed by the institution of a sophisticated governing administration. But no-one goes to Hatrasis province. Tribal politics going back over a century fuel a modern-day insurgency there, a guerrilla conflict that the Mazandaran government is quietly attempting to put down with determined military force. Provinces on the river are links in a chain, and Hatrasis cannot opt out of the chain ... and so this easy-going government wages a brutal war that is played down and hidden from the sight of the average citizen.