page 34 of 443 of Sapiens: A Brief History of Humankind

As the author demonstratd earlier, we humans can only deal socially in groups no more than 100-150 people. After that it’s too many and problems arrise. However, because we can create these fictions, we can trust that people we’ve never met, whom otherwise we would be at war with, we enter into agreements of commerce and for other services, even though they are not part of our “tribe” of 150.