Prehistory refers to the period before we have written sources. It doesn't mean that we don't have any evidence. I literally have a thousand odd pages of monographs on my desk talking about a single sort of bronze artifact in prehistoric Southeast Asia. Bands aren't tribes. Monkeys operate in bands. But it doesn't follow that monkeys operate in tribes. As I've said, the term tribe has a specific academic meaning. It doesn't just mean a group of people, although that's certainly what popular culture thinks a tribe is.