I think neals meant "modern" Christianity, as in what has become of Christianity thanks to the age of reason. This excludes some Western (especially US) branches of Christianity.
Christianity was pacifist from the beginning. Jesus was all about non-violence:
“You have heard that it was said, ‘An eye for an eye and a tooth for a tooth.’ But I say to you, Do not resist the one who is evil. But if anyone slaps you on the right cheek, turn to him the other also. - Matthew 5:38-39 ESV
I'm not sure why you're being downvoted. This was also my understanding. I highly recommend Mark Kurlansky's Nonviolence: History of a Dangerous Idea, which discusses non-violence in the history of early Christianity:
“You have heard that it was said, ‘An eye for an eye and a tooth for a tooth.’ But I say to you, Do not resist the one who is evil. But if anyone slaps you on the right cheek, turn to him the other also. - Matthew 5:38-39 ESV