Eberrontech, The Long 18th Century, and the 1970s.
So, how does this tech level work?
This third article follows up on "Why the 1970s" and "Basic Geopolitics" to explain how the technology of the world actually works, and how that connects to the 1970s themes. I've explained why I want to write a campaign setting that uses Eberron inspired magitech, but that pulls from the 1970s instead of the 1920s and 1930s. I've also discussed the geopolitics of this setting, and how that connects to the fact this world uses a Long 18th Century tech base for the magitech, rather than a Medieval tech base. As a reminder, when I say Long 18th Century for this setting, tech is around the 1830s before magitech gets involved.
Blue Collar Wizards
This is going to be explored a lot more in a further article that explores how the themes of OSR games like Shadowdark can mesh with a setting like Eberron, but the first thing to note is who does the work creating the magitech. Like Eberron, this setting has an NPC only class with basic spellcasting power, but nowhere near as much power as a PC Wizard would have. Where we differ from Eberron is, in Eberron these people belong to Dragonmarked houses, and are essentially born special. This setting does not use Dragonmarks or anything similar. Industrial magic just skilled trade you learn. I will elaborate later in that further article, but for now, The Chemical Worker's Song is a really good picture of what being one of these Blue Collar Wizards in this setting looks like. Which is to say, it's dirty, dangerous work that takes years off of your lifespan, and the rate of industrial accidents is high because magical mishaps happen. Sorta like how a lot of my coal mining ancestors died young from Black Lung and mine collapses or suffocation were an ever present threat. There is also a class divide, here, as the blue collar style of magic is more dangerous than more academic white collar magic. The 1970s is an era where both OSHA and the EPA are first established, and that can really fit with a magitech industry that's both physically dangerous and environmentally destructive.
Transportation
Railroads are the primary means of land transportation. I considered having them run off of alchemist's fire, but I think electricity is a better option. If we have alchemist's fire, we have to explain why the setting still uses sailing ships, whereas electric trains can rely on not having internal power plants. This can fit with the details about Blue Collar Wizards - magitech is sufficiently dangerous and dirty as to not want a power plant about a train or a ship. Instead, you have a separate, detached power plant that ideally can be kept away from residential areas (the word ideally bearing a lot of weight, there). You then use wires to run power to the trains. I don't think there's a reason you couldn't run power lines for rail across the American continent for freight and intercity rail if you needed to, so this shouldn't be a barrier. Also, Light Rail Transit is a 1970s phenomenon and my day job is in public transportation, so I love the little historical dig of keeping the Eberron term "lightning rail" in use, here. Eberron doesn't use any land transportation technology beyond trains, with horses still being the mainstay, and I think it makes sense to do it the same way Eberron does it. So that means no equivalents to cars or motorcycles. That doesn't mean we don't have American suburbia, suburbs first arose around the streetcar, not the automobile, these suburbs just look a bit different, being transit based.
At sea, as said, the sailing ship is the standard, at an 1830 tech level in terms of how big and heavily armed a ship can be built. I do imagine that submarines are a reality in warfare, but they'd have to be hand cranked to move, meaning we're dealing with, say, an H. L. Hunley that's actually capable of sinking a ship without sinking itself. Since this is a very short ranged design, they'd have to either be launched from shore at targets directly offshore, or carried and launched by ships. Their capabilities are, therefore, rather limited, but they are used.
In the air, the dirigible airship does exist, as does transoceanic airship transportation. They do have very limited cargo capacities, so they are really for passenger use, and cannot replace sailing ships. The military does use airships and there are airship bombing raids, but airships cannot carry anywhere near enough weapons to compete with a warship.
Domestic Technology
The standard home runs on electricity for all energy needs, including cooking and heating. Plastics exist as a byproduct of the magitech processes used to generate electricity, and are widely used in manufacturing. There is a pretty decent understanding of how to make synthetic materials. A version of television relying on some sort of magitech liquid crystal exists, allowing for mass media. The vinyl record is also in use. Radio and telephone communications are also a reality. Refrigeration works using magitech coolant fluids, and for camping, magitech heat tablets are popular stove fuel. There are electric washing and drying machines, but it's more common to own a washing machine than a drying machine. It is not rare to see families that machine wash clothes and then dry them on a clothesline. Apartments will generally have communal washing machines or rely on laundromats. Roughly half of homes have dishwashers, with them being most common in suburbs constructed in the last 30 years. Because electricity generation relies on imported energy sources, it is vulnerable to an embargo, and the analog to the 1973 Oil Embargo impacts domestic electricity use and the ability to run the rail networks. During an energy embargo, people have to heat or cool their homes less, use stoves and ovens less, and handwash dishes and clothes instead of using machines, which is of course all very irritating, and difficult for the working family. An energy embargo is something that can happen during a given adventure, but is not typically going on in the setting. It should be noted that, since electricity is generated using very dirty magical processes, the fact that domestic and transportation technology is electrified doesn't make this setting particularly green.
Medical Care
This is where things get very advanced compared to the 18th Century. There is a complex understanding of germ theory and of viruses and bacteria, meaning the mechanisms of infectious disease can be effectively combated. Vaccination is standard practice and childhood death rates are consequently very low, with parents expecting to see all of their children survive to adulthood. This understanding of infection, combined with effective anesthetics, means that complex internal surgeries can be performed with the patient expecting to survive. In a military context, this means wounded being much more likely to live than die if they make it to a hospital alive. In real life, the EKG as we would recognize it dates to 1887, and this is a setting that understands electricity specifically pretty well, so they would have things like EKG and defibrillation. I'm going to say they even figured out x-rays. The MRI machine first became available in 1974, so that could be something a few hospitals have, but most don't, because it's so cutting edge. Pharmaceuticals are where they were in the 1970s. If you get to the hospital after a major trauma, there is a ton they can do to save your life, but without automobiles and helicopters, hospital transport times really lag, and that kills a lot of patients.
What this setting is better at than the 1970s is regenerative care. Magical healing isn't faster than natural healing (this will be explained in that future article about Shadowdark's mechanics), but what it can do is heal things that weren't going to heal naturally. There is nowhere near enough supply to meet demand, however, so this tends to be elite or military healthcare, with the average civilian not getting access because they can't afford it. Even the wealthy can't necessarily get a new organ when they need one, because there aren't enough people who know how to use this sort of magic, and there is always a risk of mishaps killing patients.
Warfare
The dominant military tactics changed multiple times throughout the era in which flintlocks were the primary weapons, and in this world, they've changed again. A big driver of change is in advanced logistics. Canning, drying, dehydrating, and vacuum packing are all methods that allow for long term preservation of rations, and rail infrastructure allows complex logistics. This lets soldiers maintain long campaigns without living off of the land, and allows things like operating in winter conditions, or operating in isolated areas for long periods. Radio communications mean long distance coordination between forces is possible. Magitech gunpowder can reliably ignite even when wet, and new solvents make cleaning muskets much easier.
Combined, this means that forces tend to have significant trouble following up on battlefield victories. Opponents tend to be coordinated enough to retreat in good order rather than rout, and complex communication, logistics, and transportation systems means often being able to reinforce or block an opponent trying to exploit a breakthrough. Force generation capabilities are very high, these being industrial societies that can if necessary support millions of soldiers and thousands of ships, meaning battles can become very large and drawn out. The end result of this is wars tending to have significant attrition, often lasting several years. Trench warfare and fortress warfare is common, though maneuver warfare is also common. It should be noted that there is widespread airship reconnaissance in warfare, so concealing large troop formations is quite difficult.
Weapons wise, the conventional battlefield is dominated by muzzleloading artillery, though prolonged musketry exchanges are also a hallmark of warfare. What has fallen somewhat out of fashion is the use of the bayonet. Bayonet charges do still happen, but to a much lesser extent than they used to, and battles are typically settled by prolonged exchanges of firepower. Light infantry warfare is well understood and used where it makes sense, and a war like Vietnam is a light infantry dominated guerilla conflict.
Magitech nukes are a reality, but are unsuitable for use attacking military formations. These are very much weapons you'd use against cities or harbors. They are, of course, the ultimate, most terrifying tool available, and are a key feature in the Cold War. They have only ever been used in one conflict, just like IRL.