Violence in Christianity is a common argument used against the faith. It is alleged that Christianity is responsible for a lot of bloodshed, and therefore cannot be true. Now, the first problem with this argument is that it is circular reasoning. You cannot say Christianity is immoral, therefore it is false, any more than a Christian can say atheism is blasphemous, therefore atheists should become Christians. You must assume the truth of an alternative moral philosophy in order to use it to judge Christianity.
But more importantly, Christianity is actually not a violent religion. Christianity, as the name suggests, is a religion based on the teachings of Christ. If Christ was a violent man, or if Christ taught His followers to be violent, Christianity would be a violent religion. But Christ was not a violent man, neither did He command violence in His name. You will search the scriptures in vain for a single command to kill, injure, or otherwise abuse non-Christians.
We can, however, find commands to love our enemies and pray for our persecutors (Matthew 5:43-45), to turn the other cheek when we are offended (Matthew 5:39), to feed our enemies if they are hungry and give them drinks if they are thirsty (Romans 12:20), that those who call for violence against those who reject Jesus do not know what spirit they are of (Luke 9:55, though some manuscripts omit the specifics of the rebuke), that we must live peacefully with all as far as it depends on us (Romans 12:18) and a range of other commands for peace.
Violence and Christianity do not mix well. Of course, there are times when violence is morally acceptable. Those who are completely opposed to violence are inevitably defended by people who are not. Either that or they are wiped out by the violence they were not equipped to defend against. But spreading the faith is never an excuse for violence.
Of course, this does not mean there are no examples of violence that can be attributed to Christianity to some degree. What a faith teaches and how well its followers live out those teachings are two different things. It is even possible to claim to be a Christian, but not actually be a Christian. And indeed, one of the things that indicates a false conversion is having the wrong spirit. Violence is certainly not a fruit of the Spirit, and so a person or religion that claims to be Christian, and yet is consistently violent in faith and/or practice, could legitimately have their faith called into question.
Here is how peaceful the Christian message really is: Rather than God commanding His followers to kill His enemies, He actually sent His own Son so that His enemies could become His adopted children and inherit a place in His eternal Kingdom. You literally cannot get more peaceful than "you deserve my wrath, but I will instead offer you peace at my Son's expense". Judgement is for God to carry out after death. No Christian will ever have the right to speed up that process by killing unbelievers. If anything, we should fight to preserve the lives of unbelievers, whether to give them more chances to repent, or at least delay their eternal condemnation.
As Christians, we are ambassadors, not assassins. We encourage you to repent and believe, we do not force you to fake a smile at gunpoint. With regard to the Kingdom, we fight with our words, not our weapons. Christ is quite capable of fighting His own battles. He is just as opposed to vigilante "justice" as a human police force might be.
A note that should be unnecessary
Following the original publication of this article, three separate Calvinists alleged that it implies Christ is not God, or that He became God later in His life. To this day, I have absolutely no idea why they thought that, so I cannot specifically refute their argument, but I can expressly say that I most emphatically affirm the doctrine of the Trinity. I am hoping that these three were anomalous, but on the off chance others make the mistake, I wanted to pre-emptively dispel it.