You know what is absolutely undisputed though? America's love for guns. There are 120 guns in the US for every 100 people. American civilians own 393 million guns, both legally and otherwise, out of a worldwide total of 857 million firearms [1]. Good luck occupying that.
Also, FWIW under every circumstance that isn't some kind of military invasion phantasy porn I generally look less positively on our relationship with guns.
It seems much more likely to me that a crafty foreign power would convince the "real" Americans to fight against the "phony" Americans, whomever they may be. I believe part of the Soviet strategy was to have Americans take arms against their own government. I feel that part of the modern Russian strategy is to get Americans to be willing take arms against their neighbors. Perhaps there are other players as well who haven't made as much of a splash as the Russians in our polity.
My (admittedly uninformed and probably based on too many movies/novels) expectations would be less about traditional occupation and more about neutralization.
I can't imagine the "Red Dawn" scenario of Russian troops invading and occupying US territory. If anything, the goal would be to knock out critical communication/shipping infrastructure to effectively disrupt all normal activity--can't buy or sell, can't get food, can't depend on modern mass communication to organize and maintain order.
Alongside that, the use of modern weapons to do serious damage to centers of power would speed up collapse. That's the goal if your intention is to hit us at our weakest point: catastrophic societal collapse.
If it's our military against some other military, we've got odds as good as anyone else (and almost always better). But if you've knocked out electronic commerce, disrupted civilian use of things like cell networks and internet access, and made it hard enough to get food on supermarket shelves, all those armed people aren't gonna just keep calm and carry on while they're hungry and several cities are burning.
Sure, it's probably a bit too "straight-to-Netflix" but it's much easier for me to imagine someone applying force at the points we're weakest and letting things fall apart than facing off plane vs. plane, ship vs. ship, and tank vs. tank on the battlefield.
I imagine that the "centers of power" that would collapse would be the major metropolitan centers. We would suffer many deaths from starvation there.
But in rural areas, people would just plant a bigger garden and slaughter an extra hog or cow and dip into the canned food in the cellar. They'd also load their empty shells and sharpen their rifle skills.
Yeah. Recently I realized that alien invasion/zombie outbreak movies couldn't possibly have different setting than United States, because no other country on Earth has enough firearms just lying around for survivors to mount an armed defense against the invaders.
28 Days/Weeks/Months is a good zombie series set in the UK, it was mostly the military doing the fighting. I never could understand how zombies in the walking dead managed to overrun the US military and all their bases, many in the middle of the desert or other hard to reach places.
When it comes to zombie attacks pointy sticks seem pretty effective anyway.
Walking Dead is a TV show that makes zero sense whatsoever. I dropped watching it after 2.5 seasons, because after season 1 it lost any semblance of a plot, and became a TV-show-equivalent of the very zombies it portrays - mindlessly wandering around. I can't understand why it is so popular.
I agree that it's long overstayed its welcome, but from what I gather, the zombies are mostly irrelevant. You could swap out "zombie outbreak" with any other persistent hazard that causes the breakdown of civilization and provides a constant background threat to the actual focus of the story: the people who have to survive and deal with each other/the environment they're faced with after said breakdown.
As much as I enjoyed the early seasons, I understand that it was always the goal of the original author and the showrunners to make it more about people being people in extreme circumstances. If it was decades earlier it could just as easily have gone the Fallout route and used nuclear war/radioactive hazards/mutants/etc. as the backdrop and the stories could have stayed 95% the same.
IIRC the creator (Frank Darabont?) left after the first season, and the show has suffered tremendously since. The only reason for it's success is perhaps the love people had for zombies.
I watched a few of season 2's episodes, but gave up pretty quickly.
The problem is that, even with 393 millions of guns, USA can't stop recurrent fireforests year after year. And this is only an example. Would be naive to think that, as people have a pistol, can't be killed remotely from a million Km of distance. The idea of a foreign army marching in a country and killing people one by one like stormtroopers, is very outdated.
And of course you can always distroy critical areas and then sit and look how the civilians start killing other civilians for water or food. With so many weapons in the table would be even much faster. Is hardly a guarantee.
The succession goes grassland, scrubland, forest. The grass is indeed more flammable, but the fires are much less intense. Dry cheatgrass, for example, flares up with incredible enthusiasm, but burns to ash in literally seconds.
Also, FWIW under every circumstance that isn't some kind of military invasion phantasy porn I generally look less positively on our relationship with guns.
[1]http://www.smallarmssurvey.org/fileadmin/docs/T-Briefing-Pap...