Violence is a characteristic of many intelligent species. In fact, all, where the capacity to inflict injury and, in effect, take one's enemy out of the arena exists. Where entities seek dominance over each other, violence exists. Another factor of violence is that it is often a necessary ingredient for primitive life. Depending on the environment, violent tendencies may in fact be crucial to survival. Your Earth was such an environment. During genetic engineering projects in the past, those intelligent species developed without violent tendencies did not survive and flourish. On the contrary, they died out.
What is violence, and the tendency to use violence, and why was this a necessary ingredient in the past. First off, species eat each other. As has been often stated, the species on your planet generally use fight or flight when confronted with this possibility. Where it is assumed that these two reactions differ, they have more in common than not. Adrenaline surges, the heart beating wildly and all thought or necessity of attending to other matters, such as digestion or favoring an injury, put aside. If it is determined that fight is not possible, flight or its variant, playing dead, will be set into motion. In flight the adrenaline is put to good use in pumping legs and frantically scrambling arms. If it appears that escape is not possible, then a last attempt at deflecting the attack is tried - playing dead, or otherwise appearing as an undesirable morsel to the attacker. Thus, defecation and fainting may ensue.
Now, if fighting off the attack is possible, then a different set of staged defenses ensues. First, the defensive posture, where the body is fluffed up to appear larger or weapons such as teeth and claws are flashed. The defensive posture is quite familiar to humans, as the stiff legged circling, with neck hair fluffed and lips curled back over teeth, is seen frequently in canine pets. Humans recognize this in themselves. The refusal to sit down in a relaxed posture when in the presence of those not trusted. Hair up at the back of the neck, and not wanting the enemy to one's back. The sneer, attributed to arrogance, is in fact equivalent to curling the lips back over teeth in preparation for a fight.
Next, if the defensive posture does not succeed in deflecting the attack, taking the offensive in a parry is undertaken. The element of surprise is used as much as possible. Thus, the defensive posture is dropped and replaced with what is termed blind rage. The one under attack is now the attacker. Savage fury is unfurled. Everything in sight is devastated, without remorse or hesitation. When this defensive posture is completed, with the defendant finally spent, the attack will have either been deflected or the outcome of the battle will be in the other direction. One becomes a meal. Blind furry is seen in canine pets frequently, although it goes by different names. Humans assume their guard dogs are the aggressors, when the exact opposite is in force. The vast amount of violence in the world is related to defensive postures, even where fathers dash their crying babies against the walls. A distressing situation that cannot be dealt with in any other way may result in blind rage.
The fight or flight mechanism is not, however, the source of the violence that distresses students of human society. Regimented or ritualized violence is the horror. Soldiers marched off to war, where they are set against each other like pit bulls, forced into defensive postures against each other. Kill or be killed, not because the soldiers personally have any interest in this activity, but because elites at a distance desire territory or power. Individuals savaged as examples to others, such as the flaming tires placed around the necks of blacks in South Africa by other blacks. The message is cooperate with the whites and this is what will happen. Regimented or ritualized violence occurs because humans are intelligent enough to use the fight or flight mechanism to their advantage, quite outside of the original setting. Is one about to be eaten during territorial disputes? The fight or flight mechanism is deliberately activated by those in control of the situation, or by those who hope to be in control, more often. The elimination of ritualized or regimented violence is primarily dependent on changing the agendas of humans, which will take place gradually here on Earth during the Transformation.