So there's that change of general consciousness, and then there's this boom after the war, this expansion into the West. It was like the 1950s. The American economy was pumping at top speed. The kinds of people who would move into these communities and organize their lives around a utopian dream now had dreams about the West.

The Jacksonian era is generally talked about in terms of individualism, and the development of free market capitalism, and Victorian prudery. It was shocking to find a parallel history to that - a bunch of Americans with very different priorities. I stumbled on to these people, and then became completely fixated on them. The question that drove me was: how did these reasonable people adopt these extremely unreasonable ideas?

The thought was, 'We're going to go to California, where the soil is black and ten feet deep, and there are no rocks, and there's gold in the hills.' The West becomes the surface onto which people project their fantasies, where once the future had been the place they projected their fantasies. So it's not just the war that ends the utopian communities, but what follows.

Utopian fiction is really boring. I had to read a lot of it, and it's not that much fun. But they're fascinating to me as historical documents. Cabet [Icaria's founder and author of the utopian novel, Travels in Icaria], is writing in the 1830s, and his idea of the perfect society reveals a lot about his time. But his book is uniquely bad.

I worry that I may have overstated the impact of Civil War on the utopians. By the time the Civil War comes, most of the communities were quite separated from the wider American society. Their rhetoric is still about transforming the world, but they're not having that much traffic with their neighbors.

There are two instances I studied in which a community moved, amazingly, into an preexisting village built by other, earlier communalists. The Rappites were a German millenarian sect I mostly leave out of the story, even though they are fascinating, because they're focused on salvation and retreating from the world, as opposed to transforming it, like the other groups I write about.

These weren't college kids on acid. They were preachers, and bankers, and farmers, and the salt of American society subscribing to ideas that now seem so wild to us. These people had the most radical visions of what the future could be. And this was happening in an era we don't typically associate with sexual experimentation, or communism, or things like that.