Tribalism is generally closed, but not automatically antagonistic with other tribes. In contexts where there is no forced competition, tribes rarely fight.
The modern view is that most likely hunter-gatherer societies, which didn't have fixed lands and had no general reason to be territorial, had little warfare. It is only with agricultural societies, where competition for land becomes a factor, that we start finding evidence of warfare, as far as I understand.
Hunter gatherer societies fought all the time for control of hunting grounds.
What's interesting it's that researchers that lived with the Yanomami and other Amazonian peoples noted that most inter tribal conflicts weren't about competition for food sources-that was rather plenty- but instead for women. In polygamous societies, high status males acquired many wives and young males frequently kidnapped neighboring tribe's women which sparked constant retaliatory raids.
Humans are social creatures, but not social with the entire world.