Forgive Parasurama Karna

Can a brahmin wage war or kill someone?

Indeed, the Brahmins can go to war in an emergency or when their lives are in danger or when the situation calls for it.

The Shastras clearly allow it.

Manu Smriti, Chapter 8, Sloka 348, says:

8.348. Men born twice can take up arms when they are hindered (in the performance of their duties) (when they destroy (threaten) the twice-born castes (varna) in (evil) times.

The Yajnavalkya Smriti says similarly:

21 - 23. In an emergency, a Brahmin must perform the duties of a Kshatriya (administration and security) or the trading activities of a Vaishya. But he should not sell these items: - Fruits, Soma, silk, medicinal creepers, cottage cheese, milk, ghee, water, sesame, boiled rice, heavy metals, acids and alkalis, honey, lac, Homa, fabric, stone, utensils flowers, Vegetables, clay, leather shoes, deer skin, silk, salt, meat, oil cake, roots and perfumes.

Further:

Veda Vyasa also mentioned 'aapaddharmaas' of brahmins who render Kshatriya dharmas, Kshatriyas who perform the duties of vaishyas, and so on. [Maha Bhagavata Purana provided escape clauses related to Varnaashrama Dharma: Yasya yallakshanam drusyata tat teniva vinirdisat / In other words, the aspects of aptitude and practice can be approved. as such the principles are of a general regulative nature, while in practice the updated reflections of 'Desha-Kaala-Maana Paristhithis' would in fact prevail]

("Apaaddharmas" mean duties during an emergency.)

The Parshara Smriti (chapter 7, Sloka 35) says:

  1. Exists during a riot or in exile or when sick or unhappy the first consideration in saving one's life . The practice of religion should be postponed at this point.

The above verse can also be interpreted as Shastras, which enable brahmins to take up arms when the situation calls for it or when their lives are in danger.