I am setting up a world for a D&D campaign. Magic and technology are as usual for D&D worlds.
This world consists of a ring of hundreds of islands, in which there is one lush island that is quite large (around a million square miles). Another island in the ring is also large, about half that size, but is an inhospitable desert with few rivers or lakes. All other islands are small and are deserts or otherwise non-arable environments with no fresh water.
How can I make the desert islands worth colonizing? I need a reason for the desert islands to have been colonized to the extent that only around half of the world's population lives on the big lush island. All I can think of is mining and maybe fishing. Given that the current technological advancement is no more than Renaissance-era, I'm not sure if mining would be important enough to justify it, and
I will provide a bunch of background info below to cover most of the questions I can think of.
The Political Landscape
The lush island of Tellus is populated by many nations joined under a Tellan Confederation, with about half of the total world population. There have not been any wars on Tellus since the formation of the Confederation, but grudges persist and cooperation is often difficult, plus there is the typical D&D stuff like dragons and evil wizards and whatnot to deal with. The large desert island of Pieta was first colonized by a human nation but has since become the only island to gain independence. Now it is controlled by the Pietan Republic, a large authoritarian nation of humans, which is roughly a quarter of the world population. The Pietans only live near the coast and leave the interior unpopulated.
These two islands are in perpetual conflict (full-scale war is rare, it's usually economic and territorial competition), and vie for control of the many ring islands. What Pieta lacks in numbers, it makes up for in cooperation and determination, as it is a single unified people with a very strong and militaristic government. Pieta has no natural fertile soil of its own, so it is dependent on Tellus to import it to expand its agricultural capabilities. Additionally, the little freshwater it does have is far inland, so it is not easy to transport to the population centers, leading them to use ring island colonies to harvest rainwater.
The population of the ring islands ("ringers") consists mainly of dwarves and humans, accounting for the remaining quarter of the world's population. They are poor and, although governed as colonies of the Tellans or Pietans, they are not loyal to nor respected by either. They do hold a strong sense of camaraderie and shared struggle amongst themselves. The Coalition of Isles is an organization with the supposed goal of representing and fighting for the rights of the ringers, although usually through illegal or even unethical means. It is not officially recognized by either of the main factions and is regarded by them, as well as by many ringers, as a pirate/criminal organization.
The ring islands lack any freshwater bodies or fertile land, so food and water are very valuable and are often shipped from the less populated to the more populated islands, as well as to Pieta. Tellus values the ring islands for mining and fishing, and Pieta values them as more shorelines for farming crops and rainwater.
Although not all of this is relevant, I will provide the history of this world because people will inevitably ask for it. This isn't entirely set in stone, it's just my current idea of how things became this way.
- A large continent was inhabited by a previous civilization long ago. They used magic to make scientific discoveries and made inventions using the two together. Eventually, they discovered the atom and nuclear physics. The use of magic allowed the creation of incredibly powerful nuclear weapons, much more potent than anything ever made in the real world. The detonation of one such "thaumonuclear" weapon obliterated the entire continent, thus destroying civilization and leaving only a crater and a ring of islands behind.
- The radiation and nuclear winter that followed left all land that remained effectively inhospitable, except for the small region that became Tellus, which was somewhat shielded from the blast and ensuing effects due to a large mountain range. The number of survivors was low enough, and the time that has passed since is great enough, that all of this has since been forgotten.
- In the millennia since, the population of all races has steadily regrown and spread across Tellus, with nations growing and falling as they tend to do. Land was still abundant, so no one had a reason to venture out into the ocean much.
- About 15 centuries ago, a desert island right next to Tellus was discovered, and about 10 centuries ago other islands started being discovered. The new civilization didn't reach the technological advancement necessary for proper oceanic sailing until about 5 centuries ago, after which the ring in its entirety was discovered and (loosely) mapped.
- Pieta was slowly colonized by a human nation during this age of exploration. Around 2 centuries ago, the Pietans fought for and won their independence, organizing the Pietan Federation.
- Also during this period, warring among the Tellan nations became less frequent as the growth in technological and magical knowledge made it increasingly destructive and costly. An elven nation, which was the richest and most powerful, organized the Tellan Confederation to serve as a governing body for all of Tellus and promote peace and prosperity (and to make the elves more rich and powerful).
- In the two centuries since, the Tellan Confederacy and the Pietan Republic have colonized the ring and fought over islands, while the subjugated ringers have remained poor. The Coalition of Islands formed within the last century and has quickly gained many followers among the ringers. In the present day, everyone in the ring is either a member of the Coalition or dislikes the Coalition for its criminal reputation.