Describe a Semi-Modern/Semi-Autonomous Region

Taxes would be a big one. Who collects them, how much? Tariffs for foreign goods? Local bureaucracy would be another HUGE one, funny as that sounds. Who appoints the local tax-collector, sheriff, etc. is historically a great indicator of a country's centralization, and was something the "New Monarchs" of Europe focused on. Another thing would be laws, if the country and the region as a whole is undergoing political upheaval. Maybe there overlord is a progressive prince while they are staunch reactionaries? Or perhaps they experiment with enlightened despotism while their liege oppresses the people? Is a religious movement in place?

 

On a more social level I'd mention language [even small differences in pronunciation can make a difference], culture [customs, religion, food etc] and industries/crafts/goods. Even perceived skills and excellences play their part in creating an identity.
Spain has at least two very distinct regions that to this day are fiercely independent in spirit and attitude [Euskal Herria, The Basque Country and Catalunya, Catalonia].

 

Economy is essential. If a region can not only economically sustain itself off its own labor and resources, but create a surplus enough to export, it can exercise autonomy to a reasonable degree, regardless of whether or not there is an "imperial center" or some such external seat of power off in another region. Money is power. The only thing that could threaten such a system would be if the imperial center got smart to the economic powerhouse on its periphery and sent in the military to exploit it, probably by imposing taxes and ensuring they are paid. Probably an imperial governor will be sent in as well to watch over the political situation. In any real world historical example I can think of, this is generally the case as far as "semi-autonomous" regions go, from the Romans to the Ottomans and beyond. I mean, the United States started out as a semi-autonomous colony of England. What did England do when they needed to finance their wars? Send in the troops. And right there, should you choose to use it, is a perfect place to begin a plot.

 

Another option could be by edict. Perhaps after a particularly grueling war that engulfed the region into a period of unparalleled death and misery, a pact was forged between the different lands to separate them; give them their own identity and their own self-sufficiency. They could still technically be neighbors; (i.e. not separated by geologic features) in that they share borders, but that could be the extent of their dealings with each other. Some trade would exist undoubtedly, but perhaps it is strictly controlled to a specific caste of citizens. There would probably also be little to no emigration permitted, at least not without some form of permission (like asylum or something similar) from those in power. That way any raids might be dealt with swiftly and harshly, since each side would know the borders and expect those that stray across them to be killed.

 

Greek city states maintained loose alliances to thwart larger threats, and obviously geographic region, philosophic ideology, and religious ideology helped to forge that.

Tibet is semi-modern and while it isn't autonomous per se, it is on that world stage and of course Tibet is largely a religious region.

In the Pirates of the Caribbean movies there was that one port, of which I can't think of the name, and it's purpose was to cater to pirates and it was it's own government by powerful pirates and a similar port exists in the Starz series Black Sails.

The FARC of Columbia control large parts of the forested region in order to further their cartel needs of course and that is an open civil engagement for the Columbian government. In parallel there are the many native tribes in the Amazons or Papua who are autonomous but not at all modern.

There was believe it or not an Island off of Great Britain which a computer pirate/hacker proclaimed autonomous, as Pirateland, but supposedly a faction of the German government funded the effort to raid that island and shut it down as it legally existed in international waters.

Another big one which is semi-autonomous are the American Indian Reservations here in the States, which have their own governments in the form of councils I think, and in large part are not affected by general American law enforcement or taxation.

 

Another good example there. Look at how many corners of the world were carved up at the end of World War I (and how well that turned out).