My communities are capable of returning to Earth in Earth's past. They may go to more than one place or time, but the idea is that they will influence humankind to be population and eco-savvy, in advance of mass over population or pollution. Some of the people may have technology that would possibly be from the year 3000, but most of the re-settlers do not. The reason is that the attempt to seed other planets has failed and the only chance for Humankind is to stop Earth from being destroyed by humans.
It almost has to be a religion, but where do I place the returnees for maximum 'bang'?
That is where back in time comes into play, it has to be pre-industrial. There are approximately a thousand, but that is flexible . They have to filter through a space and that limits the number of resettlers.
North America was likely populated too late. My main protagonists started in the UK, so I would be happy to return them there. In fact, that is my preference. Is it a likely spot?
Thanks for all the answers. One gave me the idea I am going with. I've decided that the axiom 'you can lead a horse to water but you can't make him drink', is where I am going. I choose 6000 BCE in Jordan near Solomon's Mines. I'll need copper for 'my' LENR.