The bible is actually pretty clear on this one IMHO. Yes the Bible instructs us to be passive and turn the other cheek. As Christians we should ask god to show the same forgiveness for our enemies as he gives us, shown when Jesus said "Father, forgive them,". The Bible also makes it clear that it is our job to defend the defend those who are defensless and holds us responsible if we don't care for those people.
Psa 82:1-8 <A Psalm of Asaph.> God standeth in the congregation of the mighty; he judgeth among the gods. How long will ye judge unjustly, and accept the persons of the wicked? Selah. Defend the poor and fatherless: do justice to the afflicted and needy. Deliver the poor and needy: rid them out of the hand of the wicked. They know not, neither will they understand; they walk on in darkness: all the foundations of the earth are out of course. I have said, Ye are gods; and all of you are children of the most High. But ye shall die like men, and fall like one of the princes.
Arise, O God, judge the earth: for thou shalt inherit all nations.
There are also some other areas in the Bible that I believe support war in some instances but are not as clear so I won't even try. I believe it is our job as Christians to protect those who are unable to protect themselves, even if that means going to war.