Okay, so you have this other world that's overly big on prophecies and religion and whatnot. The most prevalent of these prophecies is that the Gods will return to the planet once it shines brighter than the stars themselves, as that will be the signal that the denizens of that world are finally ready to receive them. What follows, as is common with these sorts of religious fanatics, is that the world basically splits into two opposing factions that disagree on how the prophecy is supposed to be interpreted.
On the one hand you have the Infernites, who believe the prophecy can only come true when the world is burning brighter than the nearby sun which--as the people of this world all know--is itself a giant burning ball of flame. Their holy mission to is render the world aflame so that it can be seen as clearly as the stars, fulfilling the prophecy. They theorize that because such a conflagration would likely be the end of all life on the planet, they are demonstrating to the powers that be that they are not afraid to destroy everything and anything dear to them to appease said powers. Such an act of sacrifice is what the Gods demand. And, of course, the mercy of the Gods will grant them a new planet to live on afterwards. They hope.
The Auroralites, however, believe that the resolution of the prophecy requires the exact opposite: that the world needs to reflect the light of the sun to become the beacon needed to call the Gods home. In order to do this, they need to transform the entire planet to ice to achieve the maximum amount of reflective properties. By turning the world to unmoving ice, they bring about an era of peaceful silence and beautiful shimmering lights, both of which will prove to the Gods that the people have abandoned the loud aggressive ways that caused the Gods to leave in the first place.
Their ongoing struggle has been in stalemate for years, since both factions are about equal in power and number. Which is where you come in. You lead one side in this fantasy-based RTS and reclaim the world from the other cult. Both sides have an arsenal of specific weapons: The Infernites depend on machinery and explosives, devastating the continents with their flame-based weapons of science. The Auroralites depend on water and magic, specifically Ice-based, and produce and maintain the world's many seas, rivers and lakes to use against the Infernites and their structures. The Infernites also base most of their structures and units around metal, which can be endlessly melted and reformed, while the Auroralites mostly use wooden structures which can be quickly and easily grown and regrown with nature magics.
A typical Infernite mission would be to destroy all the resources of the nearby Auroralites, including the various sources of their magic (as well as pumping stations and dams) before they can retaliate. Scorching the various forests to cinders will eliminate any chance of them growing new trees in their place. Their missions therefore can be to either destroy the Auroralites operating in the area or simply turn enough of the map into unusable ash.
A typical Auroralite mission would be to eliminate an Infernite stronghold either by opening a river so it will flood a region or to simply freeze and destroy the Infernites and their structures themselves with their powerful magic. The Infernites depend on metal, which is far harder to procure for them than wood is for the Auroralites, so managing to freeze over an ore mine will cripple the Infernites operating in the area.
Both factions can also win by the brightness/reflective index, which measures how much open fire/ice is on the map at any given time (based on a % of the map covered) and awards victory to whichever side qualifies first. They will need to keep that percentage for a few minutes before a victory will be declared though. Depending on the map and various other factors (such as how bright the sun is on this map, or how cold/warm it is), these indices can often be unbalanced towards one faction, making an "index victory" for them far more tempting. If the Auroralites create too much forest (for their useful lumber), then there's a chance the Infernites can set the whole forest ablaze and achieve an easy victory. There'll be several instances like this where the index victory may jeopardize or interfere with the regular mission.
As is usual with this sort of game, defeating the game with one faction is not enough: Both campaigns must be fought through and won. Only then will the third side be unlocked: the combined forces of the various peace-loving denizens of the world who are tiring of this pointless and destructive war and wish to end it by removing both of these cults before they can enact their respective apocalyptic scenarios. Which leads to the inevitable "peace was the solution and the Gods return after heeding the spiritual brightness radiating from a harmonious world and its peoples" 'true' ending. Obviously this third side would be at a severe disadvantage on most maps, with their small numbers relying mostly on subterfuge, sabotage and making sure both sides are taken down at the same time, which is why you needed to have played through the campaigns of both cults and gained the experience first.
