[niceairport]

The vast majority of global civilian population doesn't have access to firearms.

[millipedegears]

True, but you can't fight a massively distributed attack using a very small concentrated force of professional soldiers; hence the population needs to be issued with weapons and training in an emergency for civil defense. Conventional weapons like tanks and fixed emplacements just become easy targets.

[yellowapple]

Well then maybe that, too, is a problem that needs solved?

Regardless, a slamfire shotgun only requires two pipes and a nail. Ammo is still an issue, but it's a start.