Just to piggyback on Ravenwolf’s post...
Atheists have a spiritual father whether they acknowledge him or not, the Father of Lies. He enjoys sowing strife and division to further his quest to steal, kill, and destroy. (John 10:10, James 3:15-17)
And even Christians can be influenced to do horrible things if Jesus is truly not their Lord. Note the thousands of trials, tortures, burnings at the stake, witch-hunts, persecutions, thefts, and religious wars especially in Europe in the not so distant past.
Jesus rebuked the self-righteous religious leaders of his day by saying,
“Why do you not understand what I am saying? It is because you cannot hear My word. “You are of your father the devil, and you want to do the desires of your father. He was a murderer from the beginning, and does not stand in the truth because there is no truth in him. Whenever he speaks a lie, he speaks from his own nature, for he is a liar and the father of lies. (John 8:43-44)
That is a pretty strong rebuke for the supposedly pious religious leaders.
There is a time when Christians need to take up arms and be God’s arm of judgment. David writes, “Praise be to the LORD my Rock, who trains my hands for war, my fingers for battle.” (Psalm 144:1) The Spirit-filled Christian fights recognizing the spiritual forces behind the enemy. And when motivated by Truth, Justice, and Love, always prevails with God as their Covenant-keeping Heavenly Father.
In a sense, all wars ARE religious wars, if you acknowledge that in reality every war is a spiritual conflict between Light and darkness. Of course far too many people prefer the darkness, so we have plenty of conflict.
But one day soon, this will end. We have God’s Word on that.
Just to piggyback on Ravenwolf’s post...