Second setting Protagonist

Thinking about the second D&D setting I realize at the climate at the river would be different than the mountains and the other banks.  The Plains of Caranus are not just plains.  They are a rolling flatland that does have a lot of grasslands with massive herds of animals, but it also has deep rivers in river valleys with trees, the plains would also have forests too.  There are mountains and hills but they are dwarfed by the flatness of the region.  The region close to the river gets a lot of rain, not as much as the mountains, but a lot.  The plains would without the herd animals be covered with forests.  The river valleys are cloaked with woods, but the bottoms are wide rivers that flood with the great river, or if higher flood with the season.  Many of the tributaries are thousands of kilometers long, and navigable much of their length.  (The first setting is on the headwaters of such a watershed).  Cities and city ruins are more likely to be on these rivers where they are not likely to be flooded.  The empires of old stretch along these plains and watercourses.  Societies separated by different watersheds and a plain in between can be radically different with different common languages.  

Civilizations tend to set up around water, for trade and resources, like potable water and food.  Empires stretch the river courses but sometimes across and between them, but only if they can build a rod between the expanses—which is why rivers are easier.  There are ancient roads that stretch the plains, which aids conquest and unity across the plains. But they are rare, bus cause they can so easily be lost in growing grass.  A road might be a mound in the grass in a century and just a dry spot later; a city a hill, or perhaps a small forest with a ruin at its center.  Then there are other dangers, like the lone mountain in the vast plains where no one builds because the mountain is possessed by a dragon and it views the herds on it theirs.  Habitations, towns, villages, and cities that grow too large are faced with that threat.  

And there we have the kernel of the setting.  A locality has suffered many campaigns from surrounding nations and has built its Capitol in the plateau above the frequently flooded river plains.  The plains produce a lot of food, but are hard to defend.  A small cluster of hills near a long dormant volcano that was used for centuries as a source of ore has recently been occupied by a massive dragon.  The towns near there have been abandoned in recent years and their folk have joined this kingdom as refugees, elves, dwarves, gnomes and others.  They have come and bolstered the beauty of the city, but other things have come as well.  Goblin armies of the Dragon and other minions.   The towns outside the city are besieged by the humanoids and they need to be thinned.  Moreover there are some serious threats in those armies.  The king needs people to go and fight the dragon and defeat the forces.  There are quests to find great magic to vanquish the brute.  And it is a brute. The city in the dormant volcano was larger than the home city of the adventurers and it defeated it in one day and a night.  The fires of that night lit up the night sky for hundreds of kilometers.  Stories tell that it cast spells that turned buildings to slag and the people that it killed and did not eat rose as undead in its command.  Some of the characters, if they were from that now dead city tell of the night they fled the beast how it's wings blotted out the moons in the sky, how the Dragon's tail curled around the entire city, how that night, the volcano erupted for the first time in a thousand years, the flames and lava called forth by the mighty Wyrm's presence.  The Wyrm is at once a mighty Archmage and a high priest with a thousand hit points and a hide of rubies.  It has only been a couple of decades since the attack and the dragon has slept that whole time and it's minions only hold sway over a couple hundred kilometers of the mountain and it is clear that it intends to wake soon and claim a greater swath of perhaps a thousand kilometers edge to edge.  Either way, that is bad news for the people of the city.  It is bad news for the river too.  The dragon will cut the river in half for trade maybe more.  Maybe there will be a healthy tithe of the profit or perhaps just the stop of all commerce.  The dragon is waking; the volcano belches forth smoke and ash…