Thus the group appears to us as a revival of the primal horde. Just as primitive man survives potentially in every individual, so the primal horde may arise once more out of any random collection . . .
Sigmund Freud, 1921
Freud believed that whenever people come together en masse, the uncontrollable violence characteristic of early human groups is likely to re-emerge.
"Primal horde" refers to the earliest group of humans, characterized by violence and male sexual competition.