It's human nature. We just love to belong to a group of people and think it's the bestest group of people ever.
Thanks to that we have a pretty advanced society, unlike any other being on the planet. And we also have ethnic cleansings, religious prosecution, terrorism... Also unlike any other being on the planet.
I agree that a sense of belonging is a foundational need for humans.
I disagree that the fulfillment of this need must beget violence.
If as a culture we de-emphasized dominion over others, de-emphasized reward and punishment, and instead emphasized respect to oneself and others, there would be a lot less violence.
->It's human nature. We just love to belong to a group of people and think it's the bestest group of people ever.
And this is also where Human conflict originates from. Any conflict of any kind. Bestest group decides being right is no longer enough, the other side must also be made to lose. A smaller group feels marginalized, they recruit and reach to grab power. Rest of humanity is horrified and organizes against it. Peace is restored, we sign treaties and build monuments. And then the cycle repeats.
All that to say, humans are fundamentally flawed but kind of magical beings given we have survived all cycles for over 2 million years now