You and Ray Kelly. ;')
Until that point, there were no groups to fight each other. It was strictly mano-a-mano (or, for the evolutionists here chimpo-a-chimpo).
Before the group concept took hold the size of a group that could live together was limited. A group working together can hunt/grow much more food.
I'd guess that spears were the third or fourth step in the weapons race.
The rock or stick come first, developing into the club.
Next comes the pointy stick, developing into the knife.
Then comes the LONG pointy stick, developing into the long pointy stick with a knife on it.