How did we ever manage to have so many enemies in the world: criminals, illegal immigrants, terrorists, internal subversives, nefarious politicians- the list goes on and on.
Well, when Adam ignored God’s warning and took upon himself the knowledge of good and evil, he set the stage for enemy identification for all of mankind through all of human history.
What is the difference between a friend and an enemy? Well, the one is good based on my personal opinion of good, and the other is evil based on my personal view of what is evil. One serves my purpose and advances my sense of well being; the other opposes me and my sense of well being. The concept of well being here includes much more than personal safety from harm; it also incorporates anything that threatens my comfort, financially, religiously, politically, educationally, or culturally.
Whatever does not serve my perceived self interest becomes evil and must be opposed. Those who oppose me or mine are by definition enemies. The acceptance of the knowledge of good and evil and its use to label all that hinders me as evil is the necessary element in identifying enemies. Therefore, one can conclude that the Tree of Knowledge of Good and Evil depicted in Genesis imparted to humanity the ability and necessity to create enemies. And we have been on a enemy creation spree ever since.