Does the Gita promote violence? Was the Battle of Kurukshetra seen as a "holy war?"
Krishna recognizes that violence and war are inevitable features of material existence. The material world is not a place of peace. We're here because we're envious of Krishna's supremacy, and by extension we're envious of Krishna's parts and parcels, namely, each other.
The duty of any government is to protect the citizens so that they can live peacefully and execute their religious duties. The special feature of human society and the human form of body is that by using it properly we can learn how to love and serve God.
When, inevitably, there are transgressions against peace, and disruption of people's normal duties, government must be prepared to stop those transgressions, by violence if necessary.
Specifically, the Battle of Kurukshetra was to be fought between the sons of Pandu, the Pandavas, who were all devotees of God, and dedicated to spiritual culture, and their cousins, the sons of Dhritarastra, who were not devotees, and who unfairly cheated the Pandavas of their claim to the throne. Krishna was inciting Arjuna to violence because it was Arjuna's duty to rule the kingdom and he was being prevented from doing so.
On the other hand, Krishna also makes it clear that for the soul there is neither birth nor death at any time, so even the "killing" He was recommending for Arjuna was not killing anyone, factually. (see Bhagavad-gita, 2.21, Purport)
The self is different from the body, and the greatest violence against humankind is to keep people in darkness regarding their spiritual identity, thus preventing them from understanding and serving the Supreme Person.
Often people perform violent acts in the name of religion. Such behavior is not the same as what Krishna is encouraging Arjuna to do. "Holy wars" throughout history have generally been fought by people thinking, "my religion is true and yours is not," and "therefore, I have the God-given right to kill you. God is on our side."
But if everyone truly understood and accepted Krishna's teachings in Bhagavad-gita—that we are all equal as spirit souls, that everyone's duty, regardless of faith, culture, or "religion" is to serve God—then there would be no need for fighting.