in the lands from which we declared independence long ago they had serfs that would be called into service called the fyrd to fight. this was a militia, armed with whatever implements they had with them, defending the lands of their feudal lords from invasion. they were not trained or organized, just a bunch of people with pitchforks and crap
and of course the fyrd of mercia was the one from mercia, and the fyrd of wessex came from wessex, etc. sometimes, they'd just call up the local one to deal with the local problem.
the federal government was supposed to be fairly weak, and states would be able to call up their own militias for dealing with local issues. they could also join up to deal with external threats