I'm writing a story (not sure if it's speculative fiction or low fantasy or sci-fi) that is set in a fairly realistic world except that there is a parallel dimension which humans colonized in what would be the real world's equivalent of the classical era. Portals between the worlds are naturally occurring, opening up at predictable intervals every 2 decades or so and remaining open for about half a year. With the advent of electricity, opening smaller man-made portals became possible, as well as allowing interdimensional communication. The problem is I also have an equivalent of the Americas, which I combined into a single continent a little larger than Africa. The actual story is set in this world's equivalent of the 1930s-1940s but the parallel dimension wasn't colonized until after the Americas would become populated, leaving their parallel universe counterpart completely uninhabited. The main focus of the story is actually geopolitical with a great war similar to WW2 and elements of the cold war taking a center stage, but I just realized that the existence of a whole continent that is completely uninhabited would probably have drastic effects on colonization and all of history and I am trying to figure out how to address this without absolutely destroying the rest of my worldbuilding or being forced to scrap most of what I have so far.
Too many downsides, not enough upsides and then add in a pinch of No one bothered to record it
What do I mean by that:
Well, there are many places on earth that are sparsely populated by humans - Deserts, Antarctica etc. The lack of resources and little in the way of benefits could adequately explain this situation.
Colonization is a costly process and those who partook in it were expecting to gain something:
- People/Slaves for workers/exploitation. If there are barely any people there, then this rules that out.
- Strategic/tactical considerations. Otherwise unimportant areas can be critical if they provide some tactical benefit - Gibraltar for example to the British or the Pacific Islands (and Cargo Cults) for the US in WW2 - On the inverse - New Zealand has literally zero in the way of Strategic benefit, which is why it's often forgotten about.
- Resources - To quote Al Murray 'If there's nothing in the way of Hot and Spicy food or olympic quality athletes, there's no point going' - So make your continent at least on an initial inspection to be devoid of anything useful (bonus points here for your story if it is rich in something which later on has significant usefulness)
- Arable Land and tasty wildlife - You could put this as similar to Resources - but the ability to easily grow crops or hunt game is slightly different - this is perhaps the biggest inhibitor to further exploration, there's only so much food and water you can carry with you - a reasonable 'limit' is 10 days worth of food for walking exploration. In the short-term this will provide a significant disincentive to push further but in the grander scheme of things it will limit further exploration and finally
- Lack of navigable waterways. Thomas Sowell discusses this in regards to Africa as to why African civilizations didn't 'succeed' in the way that other civilizations did (European, Chinese, Japanese etc.) and he points to the lack of rivers where goods can be ferried in bulk as one of the factors as this limits trade and slows down the transfer of materials.
Finally - If you all of those are met (and I think it can be reasonable to do so, with the right settings) - you could have a continent that is largely left alone - add in that people who did 'discover' it found nothing of interest sufficient to warrant further exploration would solve your issue.
Just make the new American continent really, really deadly. It can't be colonized by rogue individuals, everything is poisonous. The creatures, the soil, the insects. And vice versa, they cannot survive in the "Normal" World.
IN fact, that is why the Europeans in the Alternate world haven't colonized it, explorers do not return from this continent.
In the Americas, isolated, evolution resulted in an "arms race" for poisons; instead of muscles, fangs and claws, they developed toxins, immunity, then stronger toxins to overcome immunity. Animals there do not consume by eating, like a few creatures on earth they dissolvetheir prey with acids, and swallow the "soup".
People can't survive there, the only way to colonize it is a massive effort to protect themselves from the toxic life there, build shelters to keep out everything, fry the soil to sterilize it, and all the insects, creatures and plants in it, and then start from scratch with "Normal" world plants and animals. And strong water purifiers. All that would take decades to build a self-sustaining colony.
It's just not worth the trouble, either for the Europeans already there, or the Americans in the Normal world, unless there is a very compelling reason to leave the Normal America and go to the Alternate America.
In the historical 1930s and 1940s, most of the land on Earth was either a sovereign nation or claimed as a colony by a sovereign nation. Yet much of it was very thinly settled. WWII came to some of these thinly settled parts of the world ...
- Allied and Axis weather stations in the Arctic, and even airbases.
- The war in the desert.
- Anchorages and airbases in the Pacific.
So reasonably your fictional continent could play a similar role. Without population and industry, there is no military need to occupy all of it, but many sides will want to occupy strategic bits and pieces with airfields, ports, and the like. And if one side uses a location, the other side may try to prevent that use.
Having said that, I don't see a "forgotten continent" on a world with 1930s technology. There may not be recon sats and GPS, but ships and aircraft are advanced enough to produce rough maps, and then people will go there unless there is a substantial effort to prevent that.
You might get away with a population density similar to Australia a century ago, but there might still be enough for trappers from one side to notice and report the radio station being installed by the other side -- weeks or months later, as the letter finds the way to a friendly coast.