When we think about a united nations military force we have to imagine what it would represent, Unity. This force, which I will from here on refer to as the United Nations Defense Force or UNDF for short, will serve 3 purposes. 1) The unification of military might to an international body dedicated to peace and diplomatic solutions. The UNDF would be a volunteer military made up of any citizen from any UN military. It would not work for the benefit of any one nation, but the progress of peace for all. The UNDF would not take sides in conflict, but be deployed to ensure that all matters are handled with peace and with as minimal causalities as possible. The UNDF could also be deployed for peace keeping in unstable regions where warlords and dictators seek to subvert the democratic process, where freedom by the UN declaration of human rights is being repressed, or where lives are being taken on mass. Not only could this UNDF bring stability and peace to war torn and underdeveloped regions, but it would also serve as a rapid reaction response to natural disasters. 2) An end to organized military conflicts. It would be difficult for nation states to wage war when all nationstates share and depend upon a joint military dedicated to peace. 3) The intermix of cultures, religions, and philosophies. When we fight together we could understand how we all think. Fighting along side a Hindu from India, a Communist from China, an Atheist from France, and a Maasai from Africa, we could learn about our fellow man. We would have the chance to learn from others, their thoughts, their ways, their very ideals. We may find that they are not to different from us. This would be a step to a united and peaceful co existence on earth. I understand that there are MANY barriers such as language, old rivalries, corrupt governments, and something in my heart tells me that humanity is not ready yet. So I pose this question to you all. Are we ready, to unite, to stand up for something more than our selves, to take that one leap of faith, into the unknown.
Several fantasy plots have addressed the idea. The best example i've seen is in Code Geass, in which a United Federation of Nations has all of it's members relinquish native militaries, letting an independent private military organization ( a knight's order) become "the sword and shield" of member states. The U.N. could do something similar, where it has an international military, banning the upkeep of native militaries in favor of the one collective military.
Comsidering that the U.N. lacks the unity to effectively implement measures against Syrian dictator Bashar al Assad, what makes you think that they would be able to effectively take military action? It could only function if it were ran independent of every single nation. Even then, you would have serious issues with espionage as every country in the world would embed intelligence personal with the U.N. "military.