The Gītā recognises that violence and war are inevitable features of this material world. While the living entity continuously nurtures his lower instincts such as lust, anger, greed, envy etc. there will be no peace either individually or collectively. The Bhagavad-gītā is about controlling these mundane traits and cultivating our higher propensities in order to free ourselves from the bondage of saṁsāra. More can be found on this point in Bhagavad-gītā Chapter 2 – Sāṅkhya Yoga (The Yoga of Analysis)