When real Christians fight Muslims, it is because of Muslim aggression and violence. To the Muslim, it is about carrying out the mandate of the Koran. To the Christian, or Jew, or any other, it is about the duty of a human being to defend one's family and nation from tyranny.
Christians will fulfill the Great Commission through "telling the truth in love."
The problem is that the Muslims are using bombs and bullets. Not ideas.
I've read the BOOK...Christians win in the end.