You forgot to mention Alaska, Damien, don't you?

Originally Posted by The Other Guy

The Resistance groups in Poland, France, Russia, etc. managed it during WWII.

Not really, none of those groups actually "resisted" the occupation, they just found ways to really annoy the occupiers and make their stay as difficult as possible. But they could never repulse the Germans by themselves, nor did they try to.

Originally Posted by The Other Guy

The Resistance groups in Poland, France, Russia, etc. managed it during WWII.

And the civillians in those countries occupied by a brutal force all suffered from retaliations as a punishment for the activities from the resistance groups...

Originally Posted by major liability

The real question is WHY would anyone want to invade the continental United States? That's a serious question, what would anyone possibly stand to gain from such a monumental undertaking? I very much doubt the losses would be worth it in the end.

The WHY is a good question, but also HOW?

Landing on the beaches is no big deal, you just need the air superiority on the specific landing grounds.
Moving inland is no big deal, as long as you have air support and a mechanized army.

But then what?

You're standing on a tiny edge of a vast landscape, and even controlling the major cities would consume so much of an invading army that moving further and gain control over the entire country is a far fetched dream...

Only China or India could raise the manpower to get close, but they would probably be swimming around sinking vessels before they had even got close to Hawai.

Originally Posted by 84RFK

And the civillians in those countries occupied by a brutal force all suffered from retaliations as a punishment for the activities from the resistance groups...

True...

I've got resistance fighter in my blood. My great uncle was in the Polish Resistance during the war, and my great grandfater led a large disruption in crop production in Western Poland. (Of course, it almost got him shot by the Gestapo, but it didn't stop him.)

I had relatives who were Lithuanian partisans in WWII fighting both the Russians and the Germans.

Honestly, the USA probably won't be invade by foreign invaders for centuries but not in our generations.

It can be seen as true that resistance groups don't resist, they annoy and assist others to fight. The French Resistance didn't do a great deal of damage to the Germans, but they annoyed the hell out of them, however they did have an ancillary support role to allied forces eg. SOE, downed airmen and escaped POWs.

Originally Posted by AussieNick

It can be seen as true that resistance groups don't resist, they annoy and assist others to fight. The French Resistance didn't do a great deal of damage to the Germans, but they annoyed the hell out of them, however they did have an ancillary support role to allied forces eg. SOE, downed airmen and escaped POWs.

That, and sabotage, was the major task of all resistance groups in any of the occupied countries in europe during the war, at least the ones who had any source of contact with the allies.
The exception from this was the Russian and Yoguslav partisans.

Except from obvious important tasks like rescuing downed aircrews and POW's the Norwegian resistance had to get clearance from London before they went into any sort of action.

The civilian lack of cooperation with the nazi's was spontaneous though.

I suppose every Norwegian had a grandfather or other relative involved in the resistance at some point, I even know a guy whose grandfather was active in the resistance while his uncle was fighting with the Germans on the eastern front...

Resistance fighters/insurgencies will only work in two situations.

1.) The war is still being fought by two sides, in which case the insurgency helps to reduce the occupying force's ability to fight.

2.) There is an amount of political uncertainty/doubt about the mission, in which case the cost in money, material, and lives becomes enough to tip the balance in favor of leaving.

Other than those two scenarios, it is very unlikely that resistance movements will do anything more than annoy the occupiers and bring reprisals against innocent civilians. The latter is quite effective in putting out insurgencies too, either the locals give up the insurgents or they all die along with the fighters, either way problem solved.