"Some may have been in touch with the colonist society in the past, even in past centuries, and then retreated from the violence which that brought. Some may once have been part of larger tribal groups, and split off and moved away, fleeing contact. Some Amazonian groups even had guns, from intertribal trading, before they'd ever met a non-Indian. Most uncontacted tribes have used some metal tools, which they have found, stolen or traded with their neighbours, for many years or even generations.