One of the most popular, yet least respectable arguments against "religion" is that religion causes all wars. There are, of course, many variants to this. More sophisticated atheists will argue that it is only a cause of some wars. But no amount of refine can rescue this silly argument, for one simple reason: The common denominator in war is man.
It is worth noting that all Theistic religions combined have only caused about 7% of wars. That drops to a mere 3% when Islam is taken out. But even then, the question is not "was religion involved", but "was this consistent"? Although consistency is ideal, it is not a requirement for claiming a religion. You don't have to know your religion to claim it, you don't have to actively follow your religion to claim it. In fact, in my own past, I have encountered at least two people who claim to be simultaneously atheist and Christian. But this is so absurd that even these people themselves should be able to spot the flaw.
But obviously, they don't. Neither do religious warlords. Of course, if you have a religion, and especially if you're going to claim that religion, you're going to say "yeah, God is with me on this". You'd be an idiot to run around saying "our God really doesn't like what I'm doing". If your people believe it, they're not going to follow you, and if you believe it, that does rather put a damper on your plan.
Interestingly, we see this very scenario play out in 1 Kings 22. This account immediately begins by describing the motive: "Now three years passed without war between Syria and Israel. Then it came to pass, in the third year, that Jehoshaphat the king of Judah went down to visit the king of Israel. And the king of Israel said to his servants, “Do you know that Ramoth in Gilead is ours, but we hesitate to take it out of the hand of the king of Syria?” So he said to Jehoshaphat, “Will you go with me to fight at Ramoth Gilead?”" (v1-4).
So what's the motive here? It's not "a battle to see who has the best imaginary friend", as atheists scoff. The motive is territory. Syria has the territory of Ramoth in Gilead, the king of Israel wants the territory of Ramoth in Gilead, so he asks the king of Judah "hey, will you help me take this territory?"
The king of Judah, at first, agrees, but asks the king to inquire of the Lord. So the king sends for a tonne of prophets, who of course tell him what he wants to hear: "Go up, for the Lord will deliver it into the hand of the king." (v6). But this isn't actually enough for Jehosaphat, who asks "Is there not still a prophet of the Lord here, that we may inquire of Him?" (v7). The king of Israel admits "There is still one man, Micaiah the son of Imlah, by whom we may inquire of the Lord; but I hate him, because he does not prophesy good concerning me, but evil." (v8).
So, here we have a confession that there is a prophet of the Lord who has not been consulted up until now. The reason? He never tells the king what he wants to hear. But a messenger is sent to Micaiah, explicitly asking him to speak with one accord with the other prophets and encourage the king, and at first, Micaiah does so. But Jehosaphat, wanting assurance, demands "How many times shall I make you swear that you tell me nothing but the truth in the name of the Lord?" (v16). So Micaiah changes his message, not only saying Israel will lose the war, but shortly after, he reveals God's entire plan. In verse 18, Ahab basically says "see, I told you he never tells me what I want to hear". He then has the cheek to have Micaiah thrown in prison.
So what we see here is that rather than causing the war, Ahab's religion is less than an afterthought. He wanted some extra assurance, especially since this was critical in him receiving an ally, but even when God explicitly told him "look, you're going to lose, don't do it", he still ran with this strange idea that God was on his side, and he would have victory. Religion didn't cause the war. If Ahab was consistent with his religion, religion would have stopped it. But because religion wasn't the motive, the war went on until, ironically, God's word was fulfilled.
And this is how it will always be. Of course, Christianity does have a "Just War Theory". There are times when a Christian would have cause to support, or if they are in a place of authority even start a war, but the Christian faith, in general, is peaceful, stopping just shy of Pacifism. When taken seriously, this religion may well seek to finish wars, but it will never antagonistically start them. As Christ Himself said, "My kingdom is not of this world. If My kingdom were of this world, My servants would fight, so that I should not be delivered to the Jews; but now My kingdom is not from here." (Matthew 18:36).
There is one war Christians need to concern ourselves with, but as Scripture says, it is not a war of flesh and blood. Our weapons are not physical, our strategies are not carnal. Our very goal is for a Kingdom far beyond this perishing world. "For we do not wrestle against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this age, against spiritual hosts of wickedness in the heavenly places." (Ephesians 6:12).
The only ones with realistic motive to be against this particular war are those who will ultimately lose. The principalities, the powers, the rulers of darkness of this age, the spiritual hosts of wickedness in the heavenly places, these should be against this war. But only because they're on the wrong side of it. The question is, are you?
If you're using woefully uneducated arguments like "religion causes all war" as an excuse to avoid turning to Christ, the answer is yes. Of course, you are as a slave, but your captivity is of your own design. You may well be in bondage to Satan and his forces, but he doesn't need to hold you with ropes or chains. You have chosen the way of the rebel. But the good news for you is you don't have to. God is holding His fire, temporarily. But that is temporary.
Ultimately, while Scripture tells us God takes no pleasure in the death of the wicked, and that Hell itself was designed for the devil and his angels, it also tells us He was pleased to crush Jesus for our sake. The wrath due to us, God instead levied upon His Son, creating a path to reconciliation. You have been offered a passport, allowing you to freely cross the border and claim a new citizenship. Not only that, an inheritance! Heir to the King's fortune! And for no higher price than faith! Religion doesn't cause war, but you wage war against God yourself. Why not lay down your arms and repent?