The Lost Light
Khalin (kha-LEEN) is the world. A thousand years ago, an event known as the Cataclysm destroyed the gods, and thus removed all divine power from the world. Temples crumbled, clerics vanished, many paladins committed suicide or just disappeared. The undead numbers began to rise as a result, as there was no fear of retribution from paladins and clerics. A sense of good and justice was wiped off the planet, replaced with unease and fear. Ancient cities were sacked, and mankind became primitive and nomadic. The cities that remained were fortified until they were impenetrable fortresses. Darkness seized the land, and to be caught alone at night was to be dead before you knew it.
Khalin has four continents: Abaerd, Nevelen, Septech, and Quind. Quind is an uncharted frozen land mass at the north pole. Nevelen is where the campaign began, a small continent with lots of ancient secrets, home to most humans, dwarves, and elves. Abaerd is to the west of Nevelen, and is home to the dragonborn kingdoms, now shattered and in disarray, as well as large tribes of giants. Septech is to the east and slightly south of Nevelen, a land heavy with mountains and deep, dark rainforests, and is home to a large contingency of tieflings and halflings.
There are seven city-states in Khalin: two on Nevelen, three on Abaerd, one on Septech, and one on the edge of the Kirin peninsula on Quind (the barely habitable part of Quind). Each city-state is fortified to deter the undead and other creatures, and is ruled depending on their style of government.
The majority of Khalin is now broad swaths of uninhabited land, peppered with ruins of ancient cities, small, nomadic villages, and various undead enclaves. Safety is within the city-states; nowhere outside is safe.