There is, of course, no way to know this for sure because we cannot go back to “the beginning” (however you define that) and see what happens if we treat everyone “right” (however you define that). My own view is that there would have been conflict and wars among human beings no matter what. It appears to be in our nature to be selfish and greedy and those aspects of our nature will inevitably cause conflict.
I would say that the real problem is that our desire to have things our own way would have prevented us from ever agreeing on what constituted treating people “right.” Whenever two people, or two groups of people, want the same thing, they will have a hard time deciding on what the “right” way is to decide who gets it. For example, let us imagine that we wanted to treat everyone “right” and then we discovered that some countries have oil and other countries don’t. What is “right” here? Should the countries that have oil be allowed to gain all of the benefits, charging other countries for that oil? Or is it “right” for those countries to share and allow everyone to have some oil? As another example, what about fish off the coast of Portugal or Spain? Do those fish belong only to Portugal or Spain, or could people from Italy come and catch those fish as well? How far off the shore of Portugal do all the fish belong to that country?
These sorts of questions do not have any obviously correct answers. No matter how we answer them, someone is likely to feel that the outcome is unfair. Because we human beings tend to want things our own way, we tend to define “right” in ways that are beneficial to us. Therefore, even if we tried to treat everyone “right” our selfishness and greed would lead to disagreements about how to define “right” and, therefore, to conflict. For this reason, I think that conflict would have been inevitable in our world no matter how we treated people “in the beginning.”