Blessings in the Christos
I agree in spirit, ethic and principle of course, and advocate always the way of peace, but as shared by others previously, sometimes nations choose to go to war in certain situations which 'war' is serving a higher purpose by the powers the Be, and even powers above, to effect changes and transformations in the earth world and her peoples below. As I've noted,...'God' in the OT and even recognized in the NT is the sovereign Power over all, even orchestrating the tumults, conflicts and calamaties befalling mankind, and this certainly includes wars between nations, since the affairs of all world leaders are ultimately governed, directed by divine providence, even granted free will liberties,...the greater universal providence always prevails in the whole, even if some parts resist or choose not to go the higher way of life, thru love, righteousness and peace-making.
Individual followers of Jesus may choose NOT to join the military, and that is their personal choice,..but I would gather to guess a good number of those in the US military identify as some kind of 'Christian'. Some feel they are doing their duty for their country and 'God' simultaneously. What is different is only the 'opinions' on this matter. In the meantime I personally have no desire to join the military,...HOWEVER,...if there was an invasion of our country and lands and there was a serious call for citizens to rise, ARM themselves (to protect their lives and families from being killed, pillaged, destroyed, etc.).....I would consider Joining the local MILITIA in my area,...and hold the ground with my fellow countrymen. WOULD YOU? Or would you let foreign troops just ransack, pillage and murder you and your family, while you glibly stand by and do nothing? Now you see...there are sometimes where you must engage in physical self-defense...on local individual levels,...and in the greater context of nations contending with one another for one reason or another,....again back to the factor of there being 'situational-contexts' which may modify the rights and allowances of using physical force to protect oneself, or to protect others.
So,...while I'm certainly ALL ABOUT love, light, peace and human brotherhood, all under the Universal Fatherhood of God (actually a core part of Jesus true and original gospel)....I can also 'throw down' and get fierce like the Lion of Judah...when needed! In that respect, I'm gentle as a dove, but wise as a serpent, and with the art, skillfullness and intelligence given me by 'God', would be RIGHT to employ those faculties in the defense of life, recognizing its VALUE, and doing all that I can to preserve it. All else involved in considering the factors here will have to be evaluated by your own conscience. I would approach Jesus teachings with balanced discernment in light of all other universal laws and principles, then live your life with the values and loyalty to truth, as you see fit. I think we can both be reasonable enough to research our views on this, and stay open to consider aspects within the whole context, rather than just hilighting 'parts', and by doing so fail to see the forest for the trees.