Reply #1: I must presume that your question is indeed rhetorical. Because to seriously advance

[geckosfeet]

the question is to ignore human history. History is filled with violence used to advance religious, political, economic and personal agendas.

One could quibble over the word "justifiable", but that is simply a matter of perspective, a matter of whose side you are on. And of course, whomever wins the conflict is in the drivers seat. The winner generally gets to re-write history in a way that justifies their use of violence.