The Empire of Cheliax is without question one of the most powerful countries in the Inner Sea region of Golarion. Its navy effectively controls the Inner Sea, and its standing army is the largest of any in the Inner Sea region. Nevertheless, Cheliax of today is much diminished from the heights of its former Imperial glory, and many of the independent lands of the Inner Sea region are former Chelaxian holdings.
Modern Cheliax is beholden to infernal forces to retain its power. After the death of its patron god Aroden about a hundred years ago, the empire fell into 30 years of civil war, and about half of its holdings declared themselves to be independent states. The war in its central provinces was especially bloody, and in the end it was Duchess Abrogail of House Thrune who prevailed. Abrogail herself was a powerful arcane spellcaster who used summoned devils from Hell to fill the ranks of her armies. With this Infernal force, she mopped up all resistance and claimed the throne of the Empire for herself. She moved the capitol to Egorian, the seat of power of her House, and named the Church of Asmodeus as the official state religion.
The current monarch is Empress Abrogail II (great-granddaughter of Abrogail I). It is rumored that, like her great-grandmother before her, Abrogail II is a powerful arcane spellcaster. Her chief military adviser is General Gothoklek (a pit fiend), and her chief political adviser is Contessa Lrilatha (an erinyes). Both of these advisers are rumored to have been appointed by Asmodeus himself.
Slavery is widely practiced in modern Cheliax. There are many levels of slavery, from termed enslavement as a punishment for minor criminals; to life-slaves that were born into servitude. Most life-slaves are branded, generally on the face, while termed slaves wear a type of iron collar that indicates the terms. Laws regarding treatment of slaves are very complex, depending on the type of enslavement. Termed slaves cannot be maimed or killed by their masters; life-slaves have no such protection. Halflings in Cheliax are a life-slave class. While there are some free halflings in Cheliax, all need to keep their papers on them or else they risk being returned to a state of servitude.
While worship of most deities other than Asmodeus is officially tolerated in modern Cheliax, priests of other faiths are required to register with both the Church of Asmodeus and local authorities. Non-Admodean priests must agree not to speak against either the Church of Asmodeus or the Chelaxian government. Divine spellcaster of other faiths must receive a license to cast divine spells; such licenses typically list specific spells that can be cast, and the circumstances under which they can be used. Failure to comply with the very complex laws restricting other faiths can result in blasphemy charges; the penalty is usually forfeiture of all property and termed enslavement. Temples of non-Asmodean faiths are typically taxed heavily, and spies frequently attend services. Open worship of any gods of chaos is strictly forbidden.
There are pockets of resistance to the Infernal rule of House Thrune. Some nobles pay lip service to the state church, but otherwise rule their domains they way they were run before the civil war. The city of Kintargo is one such place, and the former Imperial capital of Westcrown is another.
Cheliax write-up at Pathfinder Wiki