Historically speaking, this nation was founded on "not playing by the rules" and adopting guerilla-war tactics when facing enemies on our homeland and agree with Skinny that small arms will be an intregal part of turning the modern weapons of war against an invading force.
The use of well trained marksmen and snipers has changed the advance of troops since the Civil War. The Battle of Stalingrad proved a pivotal moment during WWII when Russians faced a "superior" army.
Hope it never comes down to it but this is another primed reason that Americans should be armed. The frontier has indeed changed but it's just as dangerous.
Keep yer powder dry!
