Often when Christians make comment on the present escalating violence by radical Moslems, someone sees fit to bring up 'The Crusades" and the violence in the Old Testament as if that somehow vindicates what is happening now. Concerning the Crusades; there were two sides to that story and yes wrong things were done by the Crusaders who went to recapture the Holy Land. That was over 1,000 years ago and I think that situation is well under control now. The thing to note is that when Christians do wrong things, they are disobeying their Scriptures. Jesus doesn't condone violence but taught "Love your enemy, pray for those who despitefully use you."
What about the violence in the Old Testament? When Israel went in to possess the Promised Land, they were told to destroy the inhabitants. The Canaanites were a very depraved people. They practised bestiality among other vile sexual practices, also child sacrifice and all that went with the worship of idols. God gave them 400 years to repent, then used Israel to bring judgement. God withheld judgement for that length of time because He said, "The iniquity of the Amorites is not yet complete." Genesis 15:16. God is longsuffering. As it says in 2 Peter 3:9, He is “……not willing that any should perish but that all should come to repentance.” Iniquity is rising in Planet Earth, but rest assured it is not going unnoticed.
What is physical and natural in the Old Testament becomes spiritual in the New Testament. The enemies of God now are not people. God loves all people and Jesus died for everyone. The enemies of God are now “principalities, and powers, rulers of the darkness of this age, spiritual hosts of and wickedness in the heavenly [spiritual] places” committed to preserving Satan’s grip over the Earth and keep its inhabitants in spiritual darkness. [Ephesians 6:12] Since the Cross Satan operates illegally, his only two powers left are to deceive and accuse. He is defeated by Truth. Christ’s Army which He is raising up will bring down the devil’s strongholds in the Earth and make way for the Kingdom of God. As Jesus said “I will build My Church and the gates of Hell will not stand against it.” Matthew 16:18, 19 The Veil of darkness over the Earth will be destroyed [Isaiah 25:7-12] and Creation renewed. [Romans 8:19-21]Then at last there will be peace on Earth.
“The wolf also shall dwell with the lamb
The leopard shall lie down with the young goat….
And a little child shall lead them…..
They shall not hurt nor destroy in all My holy mountain
For the earth shall be full of the knowledge of the Lord
As the waters cover the sea.” Isaiah 11; 6-9