In fantasy, most settlements will have some archers, swordsmen, knights, and others capable of armed combat, but what we want to look at now is whether large groups of these will exist in a settlement, and why that might be. The use of technology in SF might reduce the skill and training required to operate weapons or defenses, allowing more generalized troops. Training is often required; still, this training is often more mental than physical. We’ll spend less time looking at this because those technologies and the skillsets needed to operate them are imaginary, meaning we can invent restrictions as needed for our story. Reading about considerations for existing military may give you ideas.
A larger settlement will have its local guards, or what we might call police on Earth. These individuals will have some skill, but nothing like those of more specialized warriors. This can be a sore point with them. Their reduced privilege or standing may cause jealousy, especially if they are mocked by more experienced warriors. This is a good way to add tension that occasionally erupts in a brawl, duel, or disciplinary action. These guards deal with more mundane issues among the population and less so with threats from outside. Minorities might feel unfairly targeted by them.
In fantasy, a settlement with open lands around it is likely to have a cavalry, whether this is actual knights or less armored horsemen. Unless we invent different animals, this is the fastest way to travel on land without machinery. A horse charge is a devastating tactical move. A settlement surrounded for many miles with open land is virtually certain to have cavalry (and a large one at that). But if open land is only on one side, the size of cavalry is reduced in favor of other skillsets. Horsemen still navigate forests, depending on density, and there are often trails or roads, but higher density reduces the number of troops that may pass. The same is true of mountains. Few settlements will lack horses completely unless self-powered vehicles have replaced them, so what we’re looking at here is the existence of a specialized force: cavalry.
While knights are often part of a cavalry, they may work independently of the cavalry, in circumstances where horsemanship is peripheral. Our settlement is likely to have knights if warriors with the greatest skill set and armament are needed. A settlement in the middle of a stable sovereign power without natural enemies (like an animal or monster in a nearby forest) is unlikely to have many, if any, knights in full-time residence. But if there’s a horde of something dangerous in the nearby mountain range, or the settlement lies along a contested border, we’ll have knights, and lots of them. Active war zones can change the need for such individuals, as well.
In fantasy, giant birds or dragons are two options our settlement has for an airborne military. If we decide to include creatures which are tamable to this degree in the settlement’s defenses, we need to work out their capabilities, including range. These airborne forces are more plausible in mountainous areas, due to flying creatures’ greater ease of movement there. Forests prevent them from flying, and therefore seeing, below the tree cover, but they offer an advantage even when plains or deserts surround a settlement. We might have invented flying creatures that are too small to be ridden but which can fly beneath the canopy, but this is still perilous due to the ease with which they can be shot down from hidden archers, for example.
In SF, an air force is virtually a given, with machines replacing creatures, but not always; nothing says we can’t have such exotic animals, too. This defense might have replaced cavalry and other land forces or augment them. Ships ranging in size from single-rider craft to troopships are options that give us great flexibility in what we decide is available and in what quantities, and what sort of training, if any, the riders need. It can be attractive to decide that little training is needed for one simple reason: our characters could arrive on a world which requires them to operate one of these and do so with a modicum of success, resulting in a hopefully thrilling chase on slightly unfamiliar machines through strange territory.
Consider the impact of such machines on the ability to defeat or even bypass threats on land, such as creatures capable of interfering with them. A dragon that blasts fire or ice into an engine comes to mind, but any creature able to hurl a projectile a short distance into the air can bring down a low-flying, small craft if done right. There’s a tendency to make machinery impervious to such threats; avoid this trap and your work might stand out in a good way.
The navy is easy to overlook in fantasy, as so much is focused on land and even aerial threats. In SF, the battle is typically in space, making this ignored. Regardless of genre, consider using the details found in Chapter 8, “Travel by Water,” to create a more robust presentation of naval issues. Lake-side settlements will have a decent number of ships, but their focus may be commercial rather than conquest.
The settlement’s access to lumber, if that’s the primary material for ships, will limit its shipbuilding capacity. To be a seafaring power, the country requires both sufficient wood and access to the open ocean; by contrast, if they’re located on a sea and must get past other navies to reach open water, they might be restricted to a smaller fleet. They might also become allies with a power that has a bigger navy. A settlement on the coast might be at risk for attack by ships that have cannon or a replacement for such firepower. This will mean fortifications like lighthouses, a castle, and a battery to repel an attack. Their own fleet is the best defense and keeps the fighting at sea.