They were ground dwelling, competing with animals like this for the same territory and foods.
No way they were peaceful.
Ya do not get to the top of the food chain by being passive and nice.
Humans grouped together because there was safety in numbers, safety from animals and other human beings. The most basic form of governance within a social unit is by one individual, stronger than the others, who is capable of forcing others to his will. This conflict would originate the very moment there was disagreement within the group about who got what share of food, or any other decision, and it is doubtful that those who had not even harnessed fire, flintknapping, or a wheel, were very sophisticated in their negotiating techniques. While negotiating may be more sophisticated.. a club to the head is often more efficient and certainly gets a quicker result.
A council rule (or similar) sometimes evolves as a response to tyranny under the first type of rule, but in either case, power is still in the hands of those (be they individual or group) who can FORCE their will upon those who disagree. Use of force by one group against another occured for generally the same reasons as within the group... someone had something someone else wanted, or wanted to force their will upon another... and in both cases strength and violence decided the issue if, as now, negotiation, threats, and posturing did not.
If War were to be defined as one Social Unit forcing it's will upon another, then War has existed since the dawn of mankind, and all that has changed is the scale.
Similarly, slavery has existed since the first man was able to force his will upon another... the only difference being that slavery, like war, grew more "organized" over time.
If Mankind originated in Africa.. then so did War and Slavery.