A couple classic quotations on the subject:
"War does not determine who is right - only who is left." -Bertrand Russell
"The direct use of force is such a poor solution to any problem, it is generally employed only by small children and large nations." -David Friedman
"The world has achieved brilliance without wisdom, power without conscience. Ours is a world of nuclear giants and ethical infants. We know more about war than we know about peace, more about killing that we know about living." -Omar Bradley
actually I think that last one would make a good sig quote