Spirituality never relates to violence and Bhagavad Gita is a spiritual treatise that is a harbinger of truth and peace having nothing to do with violence ever.
The contents of Bhagavad Gita, the underlying meaning can be understood only by indulgence in contemplation (chintan) which people world over failed to do. In absence of contemplation (chintan) ignorant people sometimes equated war of Mahabharata with precipitating violence. This is an absolute misnomer containing having no truth or substance.
When society reaches a point of no return and is at its lowest ebb then battle of Dharma, War of Mahabharata is the only solution. Lord Krishna precipitated battle of Mahabharata to re-establish Dharma (righteousness) against evil forces of adharma (lawlessness) prevalent everywhere.
War of Mahabharata does not occur every now and then. A battle like Mahabharata can never be equated to wars fought amongst countries even world wars.
As per Hinduism scriptures as ordained by God to re-establish Dharma advents a savior, messiah an avatar. A Mahabharata can never occur in absence of an avatar (defined as God manifest in human form).
Furthermore when Chanakya (the most able administrator in the entire history of mankind) eliminated 100 kings in one night that was also not violence! To save lives of millions of countrymen and soldiers if a few are annihilated, then as per Lord Krishna no sin or violence is committed. To re-establish Dharma (righteousness) some sacrifices are a must.