These are the five largest resistance communities in Endgame America. There are no doubt other small pockets of humanity all over the country, but for one reason or another these have met with the most success. Most people have heard of them, though rumors and hearsay are going to be more prominent than fact in many cases.
Endgame PCs are not required to be from one of these communities, but they certainly can be. Each description should give you an idea of what sort of people would come from each of them. If you have questions about the appropriateness of your character's history in regard to any of these communities, contact firstname.lastname@example.org.