Sort of.

First, a brief history of the word "bacon" itself:

According to the Oxford English Dictionary, the word "bacon" entered the English language from Old French by the 1330s. A related word also entered English from Old French, a little bit earlier: pork.

In the first instances of the word "bacon," it is essentially used as a synonym for pork, except specifically referring to the back end of the pig. That is, everything behind the shoulder - the belly, the side, the loin (the back between the shoulders and the hind legs), the thigh, and the rump.

By the end of the 1300s, though, "bacon" began to refer to these parts as being, specifically, cured/salted/preserved. If eaten fresh, then they were "pork".

And then by the early 1600s, the meaning narrowed even further, as the cured pork from the hind quarters (the rump and thigh) began to be referred to as "ham". Ham was a pre-existing word that referred to the thigh of any animal. Now it meant specifically a pig's back thigh, and specifically that this meat had been salted to be preserved.

This left "bacon" to refer to the cured meat from the belly, the side, and the loin. And to the present day, all these cuts are still often referred to as bacon in the UK. The belly-and-side cut the Americans are familiar with is "streaky bacon". The back-and-side cut that is popular for breakfast in the UK is called "back bacon" or (when specifically cut thin for frying) "rashers". There's also the cut that Americans call "Canadian bacon" which is also back bacon, but without any of the side.

But going back 200 years, all these cuts were commonly referred to as just plain "bacon," in both the US and the UK. And that's because people in both countries were commonly curing all of these cuts, and consuming them as bacon. Nowadays, in the US, the loin is often used for other purposes, such as pork chops, pork tenderloin, and (when digging a little deeper) baby back ribs.

So, yes, at least from a US perspective, what was being consumed as "bacon" 200 years ago was more varied than it is now, when it's usually the side and belly, unless it's Canadian bacon.

In your book, then, when "they took a side of bacon with them," these explorers literally took a cut of cured pork from the side of the pig, the edible meat between the belly and the loin.

clearly there was no refrigeration back then....

Well, yes, that was the original purpose. Bacon was a cured, salted meat, to preserve it without it spoiling. No refrigeration was required.

The basic process for curing bacon is essentially to rub salt into the exterior of the cut, along with spices and other flavoring agents (such as brown sugar) and let it sit this way for several days, as the salt soaks into the fresh pork. More salt/brine may be added as necessary. Then, it is smoked for many hours. That is, it is placed over a smoky fire at a low level of heat. The old-fashioned way was to hang it from a hook inside your chimney, above the fireplace.

One difference between then and now is that bacon was often cooked more thoroughly than today during the smoking process. I wouldn't say "typically," since this was most often a homemade affair. It's a bit difficult to time every cut just right, since some will be thicker or thinner. And individual families might have had preferences on how pre-cooked during the smoking process they wanted their bacon.

But you didn't want it to be too cooked. What you really were trying to do is to cook only the outside, while leaving the interior mostly uncooked. The whole point of this process was to make the exterior tough, dry, and inedible, so that food-born illnesses couldn't live on the exterior, nor make their way into the interior.

Another difference between then and now is that the rind (the skin) was usually kept on, so that would be part of the tough exterior. This way, when you went to cut off the tough exterior, you're wasting less meat, since the skin isn't really eaten as part of the bacon. In old sources, you'll often see mentions of cutting the bacon away from the rind before cooking it.

Of course, once you cut into the bacon, it would expose the part not fully cooked to potential pathogens. So, unless you planned to consume the whole slab in one sitting, you needed to do something to make sure that this end of the bacon wouldn't spoil. The basic process was, once you had cut off the portion you were going to eat for your meal, you'd cover the exposed end of the bacon with something that would keep it dry, and uninhabitable to pathogens. A lot of different substances were used, often some kind of ground grain/meal, such as cornmeal.

In Ontario, one type of bacon is still referred to as "peameal bacon" because a meal made out of peas was traditionally used for this (though today's "peameal bacon" rarely actually ever uses peameal). But you didn't even need to use food - something like sawdust could do the trick in a pinch, too.

200 years ago, this was most often a homemade job, though there would certainly also have been pig farmers selling sides, loins, and bellies of bacon at market. In the 1840s in the U.S., it became a commercial affair and big business, initially centered around Cincinnati. But by the 1850s, the big pork producers were all located in Chicago. Chicago's status as a railroad hub made it very attractive in shipping shelf-stable meat products around the country.

And bacon was one of them. Whole slabs of bacon were sold by these companies throughout the urban United States. You may have heard of a couple of these pre-Civil War companies, since they're still in business. One was Armour. Another was Swift, which might not be familiar, but their brand of frozen turkeys is - Butterball. During the Civil War, these companies (and a couple others) got big contracts to feed the Union troops, and they became some of the wealthiest companies in the country.

In the 1840s and 50s, non-electric refrigeration methods allowed for the development of early "refrigerated rail cars," which saw further innovations from that time forward. As urbanization increased in the late 19th century and methods of refrigeration became more reliable, the U.S.'s appetite for commercial bacon never subsided.

So what's the big change, then? If they didn't have to refrigerate their bacon then, why do we have to now?

The main reason is that, nowadays, bacon is usually sold pre-sliced. This was invented and patented by the Oscar Meyer company in 1924. The company had only been a small-ish Chicago operation since its founding in the late 1800s, but this innovation made them one of the major national players. The problem for consumers before this was, when buying a whole slab, you couldn't tell what the meat-to-fat ratio was until you cut into it. Sometimes you got lucky, sometimes you didn't. Once Oscar Meyer began selling pre-sliced bacon, with all slices visible, there was a lot less guess-work involved, and so consumers preferred it.

The sacrifice, as such, was that it required refrigeration. There was no leathery exterior to the bacon anymore, to protect it from pathogens. Of course, there was another advantage, too, in that Oscar Meyer could sell bacon in smaller quantities (a pound) which might only last a few days or maybe a week or two, while the larger slabs of several pounds were meant to last several weeks, or more if needed.

But if you go to a butcher or even some grocery stores nowadays, you can still by full slabs. And, theoretically at least, you shouldn't have to refrigerate - though I wouldn't trust it, since you don't know exactly how it was cured. And of course, it wouldn't work at all with uncured bacon, which usually still uses salt, but not enough to keep it from spoiling.

And because bacon is now sold pre-sliced by most major suppliers, their curing process is no longer necessarily done for preservation purposes, but rather for flavor. So quite likely, even if you could buy full slabs from some of the major bacon suppliers, it wouldn't be a good idea to store it on your counter rather than in your fridge.

TL;DR: Bacon is designed not to need refrigeration, because a full slab of bacon is protected by a dry, tough exterior that pathogens can neither live on nor penetrate. The main reason refrigeration is now required is that bacon is usually sold pre-sliced.

(Sources posted below.)