I think there is a difference between the weapons technology available today v. what was available in the 1930's. Many regulars went into battle with WWI era weaponry. The civilian arms complement was even older in many cases.

An interesting example of a 'heavily' armed society in WWII would be the Balkans region. Germany was smart; short of paras and specialist, they left the chekist and partisans to slaughter each other [sewing the seeds of the 90s conflict] as well as their Jewish populations.

To date, i can think of no example of a well/heavily armed society being invaded. There really aren't that many to pick from.