They had the logistic to cross ocean and invade mainland U.s... honest to god think typical gun gun wielding farmers gonna do shit all to tanks, bombardment, air support and trained personals with war gears... not to mention the army would have central command to do brutal overwhelming sweeps. For more effective than a farmer here and there.
Also those numbers are not accurate to ww2.
Let's be real here. Any industrial nation army would lay waste to a direction confrontation of armed civilians. It's not even close.
Anyways this doesn't really matter because by the time the U.s got into the war they were pretty capable to stopping any land invasion.