Sorry to dominate the thread but I just remembered somebody had mentioned a militia would not work well because of the size of our country.

To me, the size of our country is simply a geographical challenge that can make it more difficult for the militia or for the invader depending on how it is handled. The Swiss example is more analogous than it might seem - their area is smaller but its also very mountainous - they have a geographic challenge as well. They have learned how to use that challenge to their advantage. We could use the geography of our country - size being one factor of many - to our advantage. I just don't see how this is something that makes a militia necessarily less effective. If anything, it is an even greater challenge to any potential invader since he has even more territory he has to try and hold.