When responding to this question, we need to remember that we should not judge the teachings or the truth of a religion or philosophy by the conduct or behaviour of those who are not following those teachings.
This being the case, we need to be clear that many of the wars and other atrocities which have been committed in the name of Christ were carried out by people who either were not really Christians or who were genuine Christians but were not following the teachings of Jesus. Such conflicts were often motivated by political or economic concerns but were given religious overtones in order to convince the masses it was in their best eternal interest to get involved.
So rather than judging Christianity by the actions of these people, we should judge it by the teachings of its founder and leader, Jesus Christ. If you read through Jesus’ teachings in the Bible, you will come across such sayings as “If someone strikes you on one cheek, turn to him the other also” (Luke 6:29), “Love your enemies and pray for those who persecute you” (Matthew 5:44) and “Love your neighbour as yourself” (Matthew 19:19). Hardly the sayings of a war-mongering leader.
Another thing to remember is that war is not a problem just for Christianity. It is a problem for all religions and ideologies. More murders have been committed by atheistic regimes in this century than have been committed by any “Christian” government or organization over the past 2,000 years.
The other point to emphasize is the positive impact Christianity has made on society. This is often overlooked when people are talking about the negative things done in the name of the faith. Most of our educational institutions came out of Christianity. Many of the founders of modern science were Christians. The revivals of the 17th and 18th centuries produced social reforms that led to the abolition of slavery and the improvement of conditions for women and children. Philanthropic organizations such as the Salvation Army, the Red Cross and the YMCA came out of these revivals. Remembering this fact gives us a fuller, more balanced picture of the effect Christianity has had on society.
Read: Why Does God Allow Acts of Terror? More explanations