Personally, I do not see the necessity of a federal government, at least in the context of our current federal government. I think the biggest problems within our society is lack of participation. With what we have to our disposal, I do not see it unfeasible that a more direct democracy couldn't be obtained. You bring up something I have often wondered over. Not in the idea of an abolished federal government, but in a lesser of our current state of affairs, if we abolished the federal army in replace of our national guard unites. Air force and Navy I would imagine being a necessity to the Feds(including marines, being under the navy umbrella). But leaving it up to territories (under a more direct democracy) to vote on participation in occupying foreign land, might alleviate the exploitation of the lesser classes of our people by big business and government that seems to profit off of war. The only issue I would imagine is infighting between states without a stronger federal government. The vastness of our ecosystems, and some states lacking from other states(both in resources and talent), could arise conflict. But I would be more inclined to isolationism in being self sufficient without global trade. Thus, trading among states would be more leverage against conflict.