On the non-initiation of force

So I've been thinking some lately about the libertarian doctrine against the initiation of force, and I find that I can't square universal application of that doctrine without advocating vegetarianism. Certainly the killing of an animal(generally necessary to eat it) involves the initiation of force against another being, and I think that the natural revulsion that we most non-serial killers feel towards animal cruelty can be taken as evidence that animals should be considered as beings.

So if we take the view that eating non-human animals is OK, then perhaps we can say that the initiation of force against fellow members of a grouping to which we belong (say, mankind) is immoral. But if we can draw the line there, then can we not draw that line also at our nation's borders? If so, then an aggressive foreign policy would be justified. I kinda like this result because I feel that an aggressive (and non-belligerent) national stance serves my self interest by discouraging acts of aggression from foreign groups directed towards me.

I think that the line cannot be drawn any more restrictive than at the national border because the enforcement of non-aggression is at the national level, it would become nonsensical to apply it to any smaller group. I think that it is not useful to draw the line any less restrictive since the enforcement of it would then have to be applied by our nation on the citizens of another nation, which is, of course, a belligerent act and a violation of that nation's rights.