Before you have all those different types of soldiers, you have to get them from somewhere.
In these essays I often talk about particular aspects of culture as being on a spectrum from one option to another. This time around, though, the spectrum is almost more of a circle, with the “simplest” version in some ways looping around to resemble the most “complex” — putting quotation marks on those words because it isn’t really a matter of simplicity vs. complexity, but that’s the best way I can think of to tag them.
(And before I get into this, I want to note that to some extent I’ll be speaking of men in war. Women have also participated in combat, of course, not just in modern times but historically; however, men have formed enough of an overwhelming majority that my language here won’t always be gender-neutral.)
What do I mean by simple? If you look at your average hunter-gatherer society, you won’t find anybody you could label a “soldier.” Partly because the word “warrior” is more appropriate; the latter tends to mean someone whose permanent identity is based around being individually skilled in battle, while the former tends to mean someone whose job is to fight alongside other soldiers. But even then, warriors in this type of society don’t form a very distinct group apart from “adult men,” because war is not an activity clearly separated from the rest of daily life. The weapons of war are also the weapons of hunting, i.e. bows and arrows, spears, and so forth. Furthermore, tracking, stealth, and other hunting abilities are also used in war. There are still differences, of course — deer don’t generally shoot back or try to demoralize the enemy — but a skilled hunter is well-prepared for battle as well. And this means that when it comes time to muster forces for that battle, the majority of your adult, able-bodied men are all set to participate; all you really have to do is point them in a different direction.
Loop around to the far side, and where this almost starts to meet up again is with a standing, professional army — the sort of thing so ubiquitous in the modern world that it’s what most people think of when you say “army.” By this I mean a force of soldiers whose full-time, paid job is warfare: they may not be fighting all the time, but when a battle is in the offing, there’s no need to first extricate themselves from normal life, to get somebody to cover their shifts, mind the shop, babysit the kids. Their job is to be ready for that at a moment’s notice.
For the average modern person, unlike the average hunter-gatherer, the skills of daily life are not remotely the skills of combat. (Whatever the National Rifle Association would have you believe, we don’t rely on our proficiency with automatic rifles to feed our families. Nor are grenades a common office supply.) But here’s the similarity: both approaches mean you have military force available for use at all times. And that force is already well-trained and well-equipped, for whatever values of those words make sense in context. The cultural differences are massive — starting with that soldier/warrior distinction — but when it comes to the simple question of how ready are these people for war, there’s a bit of resemblance.
Go a bit further along the road of state development from hunter-gatherers, and you often find a different situation. The stereotypical “medieval” army in many parts of the world was based around an aristocratic warrior class who were well-trained and well-equipped for battle . . . but unlike soldiers in a standing army, they had lives and duties outside of war. So when conflict was in the offing, the king (or whoever) had to take time to muster his forces. And the way he did that was by calling in his personal followers, each of whom in turn called in their followers, and so on down the chain until somebody’s probably conscripting peasants to serve as foot soldiers. This structure, sometimes described as a “retinue of retinues,” is not so much a unified force as a hodgepodge of many smaller ones, ostensibly following the commander at the top, but in practice owing their loyalty and obedience to whoever called them in.
What about those conscripts? The generalized term here is “levy,” meaning a force that gets raised when it’s needed and disbanded when it isn’t. The actual process by which this is done and who gets levied is highly variable from society to society, so I’m not going to attempt to chase down all the different variants. But it’s important to note that in many cases, levied soldiers lack their own weapons and armor to bring with them to battle. Which means that whoever musters the army also has to scrounge up sufficient money and gear to make that army go. In the long run it’s cheaper than paying and equipping a standing army for years on end, but the results aren’t as good, because many of the men on the field have no training and have never seen battle before.
Though that isn’t always the case. The term “militia” gets used in a number of ways, including to describe paramilitary organizations that ape the structures and armament of an army without having any official blessing; in this context, however, what I mean is a local force with a certain obligation to keep themselves trained and equipped in their spare time, so that they’ll be ready when the call to battle comes. This makes them similar to the concept of a military reserve force, though the latter generally lacks that local character and receives its equipment from the standing army. Maintaining militias throughout your land shifts some of the cost downward from the crown, and ensures that when you raise levies, not all of them will be completely raw. But it also means you have a lot of armed and trained commoners; the dangers inherent in that are why not every ruler decided this was a good idea.
That fear of revolt or overthrow also applies to the last type of group I want to discuss, which is mercenaries: a professional force of experienced soldiers renting themselves out to whoever’s got a war going on right now. These often perform better than conscripts, due to training and experience. On the other hand, many people are suspicious of anybody who fights purely for pay instead of loyalty — what if the other side offers more money? In practice, mercenaries didn’t actually sell out at the drop of a hat, because doing that was a good way to ensure nobody wanted to hire you in the future. Even with that aside, though, Machiavelli argued that mercenaries wouldn’t take big risks to turn the tide of a battle, because they cared less about the cause than about being alive to collect their pay. He was also concerned that a sufficiently powerful mercenary company might just take over by force. (Not a theoretical concept for a writer in Renaissance Italy; this is how the mercenary Francisco Sforza wound up Duke of Milan).
Obviously all of this is a simplification. But I offer it up in the spirit of many of these essays, with the intent of helping to break the frame imposed by what we see in the modern world. A professional, standing army doesn’t have to be a modern thing — Rome is rather famous for its legions, nor was that the only ancient state to handle military matters in such fashion — but it also isn’t the only approach. Others have been far more common, especially in societies that can’t afford the expense of a permanent body of crack troops. Armies aren’t separate from the cultures they come from, and what civilian life looks like will affect what type of force they can (or will) bring to battle.