Islam claims to be a religion of peace. Christianity also claims to be a religion of peace. Are both claims true or is only one of the two religions truly of peace?
History is rife with people who claimed to be followers of Jesus or Muhammad while killing and plundering. To factually determine which of the two - Christianity or Islam - is the true religion of peace, bypass the people who claim to be adherents of the two religions since their claims could and have often proven to be false. Instead, start with the words and the lives of the founders of the two religions.
Is Christianity a religion of peace?
Jesus preached peace and love for one's enemies: "You have heard that it was said, ‘You shall love your neighbor and hate your enemy.’ But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you." (Matthew 5:43-44)
Did Jesus walk his talk?
According to the Bible (see Bible vs. Quran) and all other accounts of His life, including those by His detractors, He did. Jesus never hurt, maimed or killed anyone, and He certainly did not engage in war. For example, when a mob of Jews tried to crown Him king after witnessing Him perform a miracle and pressure Him to lead an armed rebellion against the Romans, Jesus walked away from them:
Then those men, when they had seen the sign that Jesus did, said, "This is truly the Prophet who is to come into the world." Therefore when Jesus perceived that they were about to come and take Him by force to make Him king, He departed again to the mountain by Himself alone. (John 6:14-15)
Jesus' pacifism is notable because Israel was being oppressed by the occupying Roman army and because Jesus had the power to defeat the Romans by force. But even when one of Jesus' disciples used violence to defend Him from being captured to be crucified, Jesus chastised His disciple, condemned violence, and healed the victim:
... Then they came and laid hands on Jesus and took Him. And suddenly, one of those who were with Jesus stretched out his hand and drew his sword, struck the servant of the high priest, and cut off his ear. But Jesus said to him, "Put your sword in its place, for all who take the sword will perish by the sword." (Matthew 26:50-52)
And one of them struck the servant of the high priest and cut off his right ear. But Jesus answered and said, "Permit even this." And He touched his ear and healed him. (Luke 22:50-51)
And while Jesus rebuked those who denied their sins, He forgave everyone who admitted theirs, even those sinning without knowledge. For example, as He was being crucified on the cross to pay the death penalty for the sins of those being saved (see True Gospel), Jesus even forgave His executioners:
And when they had come to the place called Calvary, there they crucified Him, and the criminals, one on the right hand and the other on the left. Then Jesus said, "Father, forgive them, for they do not know what they do." (Luke 23:33-34)
What about Muhammad?
While Jesus neither used nor owned a sword and warned those who did to, "Put your sword in its place, for all who take the sword will perish by the sword," Muhammad gave names to his swords. For example, after expelling the Jewish tribe of Qaynuqa from Medina in 624 AD, he gave the names, "Very Sharp," "Pluck Out," and "Death" to the three fine swords he took from them.
Did Muhammad use his swords?
Muhammad was born and raised in Mecca, a trading town, but moved to Medina, a farming town. Since there wasn't enough trading in Medina to feed his growing clan and since he didn't know how to farm, Muhammad took to plundering passing caravans and proved quite adept at it.
Emboldened by his successes, Muhammad then took to plundering towns and massacred the inhabitants of some to make others submit out of fear. He even massacred some of those who did submit. For example, when the Jews of Banu Qurayza surrendered to him in 627 AD after a 25 day siege, Muhammad had all of the approximately 900 male captives bound and beheaded.
So, when self-declared Christians kill and plunder, they are following neither the words nor the example set by Christ and therefore are not true Christians. But when Muslims kill and plunder, they are following the example and the words of Muhammad to "kill the infidels wherever you find them" (see No Compulsion in Religion and Quran).
Christianity started and grew by the power of Christ's truth and love. Islam started and grew by the fear of Muhammad’s sword. Christian martyrs give their lives to save others. Islamic martyrs die while killing others (see Islamophobia), including for not being a Muslim (see Jesus vs. Muhammad).