I don't believe we're destined to always end in death and violence, but I do recognize it is a possibility. Humans are by nature competitive and there will always be some folks who are willing to use violence to further their aims. We can put our heads in the sand and ignore that fact or we can take precautions to make us a less desirable target to predators. This is true on a person to person level and on a state to state level.
To use an analogy, the military is like car insurance. I hope I never need it, but I still have it because if I don't have it when I do need it, I'm totally screwed. Again, you can be against militarism or interventionism or imperialism. I understand those positions, but to say we shouldn't have a military at all is just a formula for disaster.