James Cameron's original 1995 "scriptment" for Avatar is probably as close as we'll get to a detailed description of how he imagined the situation on Earth unless the sequels go into this more. It starts out with this description which talks about the environmental devastation and urban sprawl, and which mentions the US still exists:
Welcome to JOSH SULLY'S world.
It is a century from now, and the population of our tired planet has tripled. Finally, drowning in its own toxic waste, starvation and poverty, the population has topped out at a nice even 20 billion.
The Earth is dying, covered with a gray mold of human civilization. Even the moon is spiderwebbed with city lights on its dark side. Overpopulation, over-development, nuclear terrorism, environmental warfare tactics, radiation leakage from power plants and waste dumps, toxic waste, air pollution, deforestation, pollution and overfishing of the oceans, global warming, ozone depletion, loss of biodiversity through extinction... all of these have combined to make the once green and beautiful planet a terminal cess-pool.
Josh lives in the urban sprawl which has grown like kudzu over the whole eastern US.
His particular part of this undifferentiated concrete rat-warren is Charlotte, NC, but you could be anywhere. Its the same crowded, gray, trash-strewn high-tech squalor. The walls are gray, the sky is gray... the people are gray.
They shuffle past each other in dense crowds, shoulder to shoulder, unwashed because of the water shortages, and sickly looking from the bankrupt diet of cheap carbohydrates and synthetic proteins. It looks like a cross between THX-1138 and a Calcutta train station.
It also says Sully was paralyzed in "a stupid little war people barely remember" and says the crowd ignores him as "another angry vet" but doesn't go into any more details on the conflict. A little more on the overall world situation appears in the discussion of the news report seen on the TV in his "tiny cubicle of an apartment in a vast government housing project":
The oceans are overfished and barren, poisoned by toxic runoff. All whales and at least half the Earth's fish species are extinct. On land over half the species extant at the beginning of the century are now gone forever, with most of the remaining endangered.
The human race, using its technical ingenuity, has learned to keep itself alive, but it has lost almost all contact with the natural world, which it has strangled and crushed out of existence. There are no national parks left, only housing projects and protein farms. Yosemite is an upscale condo development. Most ocean-front property is used for mari-culture, since the only food source efficient enough to feed everyone these days is spirulina. It's amazing the things you can do with algal protein concentrate if you know your spices.
And a little later Sully meets representatives of the RDA, described as a "international consortium of major corporations" rather than a single company:
They tell him they are with the RDA, the RESOURCES DEVELOPMENT ALLIANCE. This is an international consortium of major corporations whose purpose is to find and exploit resources on other planets, both within the solar system, and in the last 25 years, among the nearer star systems. Imagine the Dutch West India Company funded by Microsoft, Matsushita and a dozen or so of their megacorporation buddies. Everyone just calls it "THE CONSORTIUM".
The RDA has an official charter from the ICA, the Interplanetary Commerce Administration (pronounced eye-kah), an international trade-regulating body run much like the EC is today. The charter allows them to exploit the The RDA has an official charter from the ICA, the Interplanetary Commerce Administration (pronounced eye-kah), an international trade-regulating body run much like the EC is today. The charter allows them to exploit the resources of planets, moons, asteroids... whatever they find... as long as they follow the International Space Resources Treaty, and the other treaties which prohibit weapons of mass destruction and limit military power in space.
When Avatar came out there was an official site called "Pandorapedia" that contained long entries on different aspects of the movie, the site still exists but unfortunately most of that information has been removed, luckily archive.org has copies of many entries saved. The entry on the RDA seems to say it was changed to be a single corporation, calling it a "Massive corporation involved in interests ranging from mining, transportation, medicines, weapons and communications" and saying:
With millions of shareholders, RDA is the oldest and largest of the quasi-governmental administrative entities (QGAEs). But its origins are far more modest. The entity that would become RDA was little more than a Silicon Valley garage startup in the early 21st century, when its two founders borrowed money from family members to begin the company.
Within a few decades, the company had the stature to propose the construction of a world-spanning rapid transit system that would allow entire population groups to conveniently commute hundreds or even thousands of miles to perform work where it was needed, without impinging on the cultural values of host populations. This led to the current global network of maglev trains that require the superconductor unobtanium for their continued operation.
The scriptment's description of the interstellar spaceship indicates it's hugely expensive, so they need to be mining and manufacturing extremely valuable products on Pandora to justify the cost:
You have to go really fast. Almost as fast as the absolute laws of physics permit. And you have to use more energy to reach that speed (and then slow back down) than all of human civilization is currently using in a year. So the bottom line is... the bottom line. Money. A lot of money.
About a million dollars a pound, to get something from Pandora back to Earth. The object of the game is not to go there and mine coal. You want to find things that don't exist in our solar system at all or are incredibly rare, and then you want to refine and process those raw materials, so that what you send back is the finished product.
It goes on to say they were trying to train the Na'avi to do the work of refining and processing, since human workers would be too hard to ship and would immediately die without their oxygen masks, but this seems to be an element that was changed between the scriptment and the finished movie, and the reasons might tell us a little more about the technology and economy of Earth. The "Unobtanium Mine and Refinery" section from the RDA Entry of Pandorapedia makes no mention of Na'vi workers, and says "The mine and refinery complex is relatively untroubled by Pandoran life forms, with automatic machine guns on guard towers easily able to easily able to cope with marauding ground and air attackers." The entry on the ISV Venture Star has some details that match the scriptment like the statement that it was manufactured by a "Consortium of aerospace contractors under control of RDA" and also mention that part of the value of unobtanium is that it's needed to "contain and direct" the matter/antimatter reactions that provide thrust:
The ships of this class are not exploration ships, they are commercial freighters. The ship's mission is to be part of an endlessly looping supply chain which enables the exploitation of the indigenous resources of Pandora. The ISV Venture Star, and the other ships of its class, represent the highest technological achievement in human history. Only the great need for unobtanium and the energy which it allows human civilization to produce could justify the cost of creating these vessels. In fact, the unobtanium itself enabled the creation of this class of ISV’s. It is used in the superconducting magnet arrays which contain and direct the energy of the matter-antimatter annihilation which propels the ship. Without unobtanium, interstellar commerce on this scale would not be possible. Unobtanium is not only the key to Earth’s energy needs in the 22nd century, but it is the enabler of interstellar travel and the establishment of a truly spacefaring civilization.
Part of this entry also indicates that part of the cargo inbound to Pandora was a form of highly or fully automated manufacturing system, which could presumably take the place of the Na'vi workers from the scriptment:
Universal object-manufacturing system (In-situ Stereolighography plant). This can produce large, complex objects from data describing their three-dimensional form and material composition. Using raw materials obtained on Pandora, construction and mining equipment far too large and massive to be shipped from Earth can be produced, along with any replacement parts that are needed. Smaller items such as weapons and furniture, are also created, using design data brought from Earth. Locally-designed items are made as well, or modifications of existing designs.
Micro-miniaturized components like mirco- and nanoprocessors and other circuitry elements that cannot be manufactured on Pandora.
This mention of highly automated manufacture is echoed in the tie-in book Avatar: The Way of Water: The Visual Dictionary, which has an entry for "Shipyard Factory 3D Printing" which says:
Exploiting and colonizing Pandora requires an incredible tonnage of material and equipment, most of which cannot practically be shipped to the new world by ISV. Transporting heavy materials requires accelerating them to 70 percent of the speed of light (and decelerating them, too), so harvesting and building is done on-world wherever possible. The key to a quick and efficient strategy is rapid manufacturing, primarily enabled by advanced 3D printing techniques. With metals and petrochemicals extracted from Pandora, 3D printers can churn out vast numbers of components for vehicles, weapons, robotics, data equipment, and even buildings, which are then fed into rapid, highly automated assembly lines.
An accompany "fact file" info box also echoes item 2 from the ISV Venture Star Pandorapedia entry quoted earlier in saying "Not all RDA equipment can be printed on Pandora. Sophisticated quantum electronics and other microscale components are shipped from Earth." It also adds "While manufacturing is as automated as possible, human assistance is always required to deal with inevitable unexpected problems." So apart from giving a canon answer to why they don't need Na'vi workers as in the scriptment, this could also be seen as an explanation for Earth is not a post-scarcity economy where machines can replicate copies of all needed goods (including the manufacturing machines themselves) for no more than the costs of raw materials and energy. On the other hand, the high degree of automation in mining and manufacturing, perhaps including projects done mostly away from the surface of any habitable world like Earth or Pandora (James Cameron himself once invested in asteroid mining) could help explain how a dying world is able to build massive space projects like the ISV Venture Star.