ugh
first and foremost, one must understand human nature before you can try and decide how to run a country.
taking that into account, you must then understand you cannot merely maintain a world order, as a country that stands at the top of the world, and live on a 'if they attack our soil and invade, we'll defend' style of warfare. one must use offensive attacks to maintain order and peace.
there will always be groups that will attempt to destroy the foundation of the country. if you let them attack, and if they didn't invade, just stand there.. sooner or later the country will collapse under its own weight without that foundation.
now if they attack and you go to their soil and attack, that should always be permissible.
so should preventive offensive strikes, such as going to a country (with the knowledge they want to attack you), and prevent them from attacking you by any means necessary.
and accept it, until the U.N. can step in and actually do the job it was designated to do, which is maintain peace across the world, then someone is going to have to maintain order. and until the U.N. can step up, the powerful 'western' countries will always have a target on their backs from the smaller lesser-developed states and from small cell networks.
all because of human nature. We are a tribal entity, and at every step of life there is a drive to be the dominant.
and as far as a state having a military, it will be required due to the above statements. and freedom will always require the sacrifice of a few into the woodwork of this state to keep it running as is. to say otherwise is a testament to your ignorance, naiveness, and lack of understanding of how the world truly operates. you can dream of going back in time and changing the nature of governments and how things operate, but it will almost exactly be the same way as it is now, except maybe under a different hegemony. to dramatically change the world, religion would have to be rid of. The terrorists likely wouldn't even exist, at least not with their current motives, if religion were never created and in fact completely prevented.
but that is for another debate that has actually occurred many a time already.