Harry Turtledove. Noninterference (1987)

     Harry Turtledove. Noninterference (1987) The Survey Service is on Bilbeis V. The local Queen is sick of cancer. One of the anthropologists persuades his team mates to give her immunity boosters to destroy the cancer. They leave. 1500 years later, a routine resurvey discovers the Queen is still alive, and revered as a goddess. She has brought her people from early iron age to approximately medieval levels of technology. The report is suppressed for political reasons: factions within the Federacy want to stop all exploration of extra-Federacy planets. All except one of the survey team is murdered in order to keep the report secret, but eventually a second follow-up expedition is dispatched. After much plotting and more or less bloody action, the bad guys get theirs, and the Queen is left musing about star people. She plans to visit them before they come back again.
     Turtledove is good on bureaucratic machinations and on the effects of even slight cultural contacts. The plotting is intricate, and develops from the characters. His characterisation is strong enough that we care about what happens to the protagonists, but it doesn’t of course get in the way of the essence of the book, which is an exploration of cultural evolution. He suggests that it is not merely the institutions that determine how a society evolves, but also the presence or absence or strong personalities at key positions in those institutions. In this, he belongs to the contingency school: general principles govern social (and other evolution), but accidents of one kind or another can and do divert it into unexpected and, more importantly, unpredictable directions. The stream always flows downhill; but if it’s blocked, or a barrier is removed, the stream will change direction, sometimes drastically. A good read, but not a keeper. **½. (2002)
     Update 2013: Turtledove is also known as an alternate history writer. this book really belongs in that genre, despite its SF trappings.