Rogue
The opening line in the Player's Handbook states "Rogues have little in common with one another." This is completely wrong.
Rogues most certainly have much in common with each other. Beyond the obvious need to work outside of the natural framework of imposed laws, the PHB gives a long list of potential professions of rogues. Rogues in Arthea are well organised; without organisation there would be no organised crime. Some criminal gangs in Arthea really like organised crime.
There are differing degrees to this organisation around the kingdoms of the land. Ticetia has the best organised criminals, this situation has persisted from the days when the crown of Arthea was passed to the Ticetians. There is no big city that isn't controlled by a multitude of criminal gangs and organisations. This behaviour has begun to spread to Caldonacia too. In Ticetia and western Caldonacia it is virtually impossible to operate as a thief alone. If the organised criminals find out, they make no habit of leniency. Only in the former Empire is it still feasible to follow a career as a solo rogue.
This doesn't make it impossible to form a new criminal organisation in the north. New gangs turn up all the time, often from some of the pieces of a rogues guild that could no longer agree. Establishing a new guild would take a little effort, and most rogues would struggle to carry out that task alone - they'd be relying on the co-operation of their friends.
Selection of thief guild is an important one for player characters. If an individual is planning a career as a rogue, then they would do well to learn their trade from those who are already working it. Rogues can, of course, train themselves - but learning is far quicker when instructed by a master. Just remember that on one hand there is no honour among thieves, while on the other there is no trust either.