A few weeks ago I finished the "Island in the Sea of Time" series. This is a trilogy by S. M. Stirling. If you read my review of "Dies the Fire", then you know that I enjoy his stories but find his writing a bit lacking. What is interesting is that this series, which is older than the other books I read by Stirling, is much better written than his newer books.
The premise is rather simple. Some event engulfs the island of Nantucket and sends the island (and all it's inhabitants) back in time three thousand years. The series details how the islanders survive and begin to deal with the world around them. Unlike Stirling's other books where he seems to spend pages upon pages talking about grass (seriously), this series has a great deal more action and excitement to it.
Without giving too much away, the technology and knowledge of the islanders allows them to gain quite a bit of power in the ancient world and history is forever changed by their impact.
I'm a huge fan of alternate history books, and I really enjoy how Stirling writes in this genre. For example, Conquistador deals with both our world and and a world with an alternate history. Despite what I think of his newer writings, I'll probably pick up all his books over time.
One last note. In "Dies the Fire", something happens to make all technology stop working. This series deals with the world that Nantucket left behind in the other series. Outside of that though there is no other connection between the two series.