Sort of. The big advantage the US had was OCEANS on both sides and only stone age peoples to the south. Attacking the US on it's own soil has been a suicide mission for hundreds of years. Counties in order to attack the US would need to pile men on ships travel for a month(s) then attempt to skirmish on the beaches. On the other hand attacking Poland /Korea/China/Spain/Italy/Egypt is a matter of walking. Once ships were powered/quick enough to transfer men in mass it was too late -- the repeating rifle had been invented.