The conquests have, in short, left Serbia grossly overextended, especially in Asia - the giant buffer zone was indeed ungovernable in reality - the instant Dušan turned around and left an area, it would fall into anarchy, which could allow the Turks to return. Uroš realized that the only way to permanently secure that flank is to completely subjugate it. But that was for now, completely impossible - there simply were no means to do so, and the conquests have bled the country dry, despite the profitability of the various mines, and the wealth that passing traders brought in. All the mercenaries had to be paid - most were, but there still were a couple of debts left, and of course, to pay for the rented navy used in the endeavor. Another problem was the fact that the countryside was severely underdeveloped infrastructure-wise, apart from the areas closest to the main trade routes, and swarming with thieves and brigands. The new territories were rather chaotic as well. The Greeks were quickly becoming culturally domineering due to their lands being the most developed, and their historic dominance.
The first order of business was to move the Imperial capital to Belgrade, both to remove himself maximally from Greek influence, and due to the strategic location. Previously Belgrade was more of a underdeveloped fort, but with excellent potential for trade, in part due to the easy access to the Danube and Sava rivers and the Morava valley. Another reason is to signal to other European powers that the Pannonian basin was now Serbia's backyard. Another reason to choose it over the much more prestigious Constantinople was the fact that for whatever reason, Uroš, unlike his father, was completely uninterested in having Byzantium live through Serbia. In his eyes, Serbia completely replaced Byzantium, and had little to do with the state. A rather large palace was planned, but only a small building was built, to which other segments would be added when funds became available. A new city was founded as well, on the mouth of the Morava - Dušanovgrad in 1379. It would remain small, but an favored stopover for traders, due to being on the junction of the eastward Danube road and southward Morava road.
The second order of business was to combat the underdevelopment of the non-Greek parts of the Empire. Uroš dealt with this by at first repairing, expanding and standardizing major roads, which mostly followed ancient Roman ones, starting in 1374. As money started to accumulate again, the project sped up considerably - it would almost be complete by 1390. This improved the accessibility of the country greatly, allowed the harbors - many of which were ordered to be built or renovated by Dušan even prior to his conquest of Constantinople, and were just completed now, to flourish - the quickest-growing one being a new port on the mouth of the Bojana river, Sveti Nikola, which was prior the sea port of Skadar, a little bit upstream, but after the renovation, fell under the control of much closer Ulcinj. However, as the settlement grew, it would eventually get city rights in 1387. The entire area would experience major development. Other ports would see major development as well, such as Athens and Thessaloniki. A coast road was arranged with Dubrovnik and Venice as well, and this road would be completed in 1380. It was particularly useful for getting goods from the short section of Dalmatian coast owned by Serbia into Dubrovnik or Venetian Dalmatia by land, helped improve relations with Venice (certain debts got cleared), and will prove very useful later on.
Another problem was the rampart banditry that was a constant problem in everyday functioning of the state. Dušan tried dealing with this issue in his Code, by instituting punishments for settlements and villages that are found to have bandits in them, up to completely scattering the village, with the inhabitants being forced to pay the damages of course. The problem was, the fact that the law, in general, was very weakly enforced. A great amount of funds were spent to combat this issue, and crime was dealt with severely - Uroš made his own modification of the Code in 1378 - this new code was virtually identical to the previous, but with certain major changes: the Greek-based titles as established by Dušan were purged, replaced with Serbian ones (for example, kefalija returned to it's previous form, Župan), the Byzantine punishments such as executions and mutilations were replaced not with the traditional Serbian fines, but something new: enslavement. Another change was the purging of Albanians and Vlachs as social classes of their own, something that was previously in effect due to their primarily pastoral lifestyle. Now, all pastoral inhabitants were considered equal. This was mostly done as the previously large amount of pastoralists reduced significantly after the war - many Vlachs and Albanians found better work in other fields now opened up due to the casualties in the war. At last, but not the least, the nobility was greatly curtailed in their power. This made the inner workings of the state much more efficient, and the tax collection was significantly increased, though there were grumblings of course, especially by the Greeks and the nobility, but none of them were in the mood for rebellion.
The biggest thorn in the side for Uroš were the Greeks. As mentioned, Uroš has a heavy distaste for their immense influence - the biggest of which being in culture. The Greeks were extremely well-educated, and the only thing close to academia was the Pandidakterion in Constantinople. Highest tiers of education were only possible with personal tutors, and for the clergy. And the clergy were heavily hellenized already. Inspired by the Pandidakterion, and the unusual corporate universities of the west - Uroš would establish the sveučilište [1] in Belgrade in 1382. But unlike all other such institutions, it was completely secular, and not administrated by church authorities, but by the state itself [2], and was open to anyone who could pay the price (which was initially quite steep). Another major difference is that neither Latin nor Greek were taught there, except for translation purposes - the line between the standard language and common language pretty much became blurred [3] as ancient books started to be translated into Serbian, all due to the stubborn attempts by Uroš to impose a new cultural elite. Schools started popping up everywhere, even in villages, just like in former Byzantium.
Another part of this plan to weaken the Greek component of the Empire was to scatter them. And the solution was extremely simple - all over the Empire, there were hundreds of estates now lying abandoned. Putting the autocrat in his title to test, Uroš, instead of giving this to the large landowners of the nobility, made a proclamation: free land for settlers! But they weren't told that they would be assigned plots located in the middle of nowhere most of the time. Greek new landowners found themselves moving north into Bulgaria and Serbia. A particularly diverse mix found itself in Serbian Pannonia (what the bit of Hungary Serbia took started being called), Greeks even being a plurality in Bačka at one point. A very high amount of Catholic Croats suddenly found themselves owning huge estates all the way on the Pelopponese, and Anatolia. Hungarian villages sprung up in Epirus and Thrace. Albanians appeared in Bulgaria. A few Turks who converted to Orthodoxy moved into Croatia. This greatly boosted the population of the Slavic northern bit of the Empire, but the Greeks were so numerous it didn't harm their powerful position much. And the nobility now got really pissed, but were still too weak to do any harm.
In 1389, Uroš would start 2 projects - the strengthening of the rather small Serbian navy, and the proliferation of gunpowder weapons that were spreading. The Greek Fire was extremely useful and horrified enemies, but the mixture was prohibitively expensive, the machines clunky, could not break fortifications (though they could clear some fortification designs out easier due to impressive reach), and was heavily vulnerable to projectile weapons, such as cannons, catapults and trebuchets. When hit, the device would explode, sending fiery oil in all directions, turning the using army into roast. And even worse, during the end stages of the war, the enemies learned that vinegar-soaked hides and felt would render the substance ineffective. Cannons, on the other hand, even though they couldn't spread as much devastation, had the physical power and accuracy that was needed, and they were cheaper to use (though not to produce). Cannon foundries and gunpowder mills started popping up around the country - Constantinople notably became a center of production of such weapons, but most cannons used by Serbia came out of Trgovište [4], and the gunpowder from Velbužd [5].
Not to be ignored is the marriage between Strahinja and young Katarina (Catherine) of Hungary in 1383, Strahinja being 16 years old and Katarina 17. The ceremony happened in the Hagia Sophia, of course. Strahinja would move to Budim (Buda) and rule the Kingdom of Hungary, which he already saw as a part of Serbia anyway. Other European powers were reasonably upset at this - especially the Pope. As Strahinja took over and the regency council left, the Czechs, now under the rule of the rather weak Wenceslaus IV, and Austrians, led by Albert III and Leopold III, started to turn more anti-Serbian. But Strahinja had ambitions of his own - to take back Upper Hungary (Slovakia) first and foremost. However, no conflicts would occur - everyone was busy with other things for the time being.
Both Strahinja and 12 year old Rastko proved to be extremely intelligent, and many saw more Dušan than Uroš in them. However, their sisters were... different. 20 years old at the time of Strahinja's marriage, none of them were married. Nobody wanted them, really, and for good reason. Extremely tall like their father, they had a constant appearance of extreme illness, with deathly pale skin and dark circles around their brown eyes. Their brown hair was dry and lifeless as straw, and they were dangerously thin. But that wasn't all - their large brown eyes had a distinct piercing, but somewhat distant and lifeless stare that made everyone uncomfortable. But apart from that, they were extremely intelligent and cunning - when they were lucid that is...
*******
Nerodimlje, a sunny August day in 1383, just a few weeks after Strahinja's wedding and departure
"It's so boring here. Strahinja's wedding was awesome! So many colors, so many people! So many cute princesses of my age, hehe." Thought Rastko to himself.
The palaces of Nerodimlje were pretty large, but very simple and utilitarian, with only some decoration haphazardly added over time. And now the complex mostly stood empty, only the building of the local župan was a lively place, and only when the man was actually there. At those moments, many people would gather with various reports, petitions, requests, gifts, demands and such things and he would solve them. He has two kids - a 5 year old son, Marko and an impossibly fat 16-year old daughter, Poleksija, who's supposed to marry some rather influential Christian Turk called Demir, son of some Orhan who's apparently extremely influential in that wild borderland. Demir came by once, funny man - very dark skin and a hooked nose, with an Asiatic haircut and a large mustache, and his Serbian was very strange. He didn't seem to mind that young Poleksija was so large that she took up the entire doorway. It's normal that women fatten up in preparation for carrying a child, but Poleksija doesn't have that issue. This Demir guy wasn't actually there to inspect his future wife, but to take care of some business with Uroš. But that was before Strahinja's wedding. Anyway, when the župan's kids were there, Rastko would be very happy - they were always eager to play, and despite the fact that little Marko was a little too young, and Poleksija too mature. But it beat socializing with his sisters, they're weird and only read books.
Rastko's train of thought would be interrupted by the little Marko. "Do you want to play, Rastko?" The boy asked.
"How in God's name did you get in here?" The palace doors were locked, there is no way to get in. "Isn't Poleksija supposed to keep a watch on you?"
"I found a way only I can use!" Marko said jovially.
This interested Rastko greatly. "Care to show me? Maybe I can go through it."
Not even replying, the little boy started running down the hall. He eventually reached Isidora's room, and went out on the balcony. Suddenly the boy jumped the wall and started walking on the narrow ledge. He quickly grabs the boy and drags him back over to the balcony. Rastko then figured out that the boy used the rather old courtyard wall to reach a very thin ledge that led to the balcony. He's a very agile boy. Maybe he should give some to his sister, who's nowhere to be seen.
"Aargh!" and the sound of something pretty heavy hitting the bushes. A few moments later, Poleksija, all dirty, walks into view, sobbing. "Stupid boy... Father's gonna kill me! Oh God I hope he got in and is fine..."
"You lookin' for this little mischief-maker?"
Poleksija's face suddenly contorted into her trademark grin. "Oh praise the Lord! I grew so desperate I tried to follow him. Naturally, the loose bricks couldn't handle my greatness." She said smugly.
Isidora appears behind them silently as a ghost. Her paleness is increased so due to her completely white clothes. "Now what are you boys doing here? Don't you know it's uncultured to intrude into other people's rooms uninvited?" She looks relatively normal, and she asked the question in a non-serious tone.
Marko turned white. "S-sorry!" He mumbled.
"Teehee, you truly are a little devil, Marko" She said, touching Marko on the nose with her finger playfully
From that point on, Rastko stopped listening. Isidora and Poleksija were talking about some boring things, and started bantering with eachother about something. Rastko wasn't listening and was preoccupied with playing some gesturing game with Marko, until Isidora joked about Poleksija's ludicrous weight. To this Poleksija replied something about her getting married soon, and that obviously Isidora should pick up the fork as well, as if she continues like this, she's going to die alone. Both laughed, but then tears filled Isidora's eyes. This Rastko noticed, and already knew what was going to happen. She started sobbing, then collapsed on her knees. Her eyes went up and only whites were visible, and then she started screaming and speaking gibberish, and tried to throw herself off the balcony, and Rastko, who is built rather powerfully for a 12 year old, just barely managed to hold her back. She then grabs Marko who starts crying and holds him over the wall, her stick-thin, long bony arms shaking, unable to deal with the boy's mass, to which Poleksija simply faints. Rastko then jumps and grabs his enraged sister in a choke hold, which makes her drop Marko back onto the balcony. At this point Isidora calms down, curls up in her bed and upon realizing what she tried to do, starts sobbing uncontrollably, cursing herself, calling herself the most terrible things. Rastko tries to console her, but to no avail, she starts crying even more.
He then takes Marko outside to the shaken Poleksija who just came back to herself, and shot up like an arrow when she saw that Marko is safe. She then runs towards them and grabs the boy.
"Oh thank God and all the saints! I feel bad for your sisters Rastko, truly poor things they are. I have never met smarter people, but all good things come with a curse I guess. I pray for their curing every day."
Such things were normal and happened almost every day. And there were no rules. Sometimes the sisters would get into terribly long and tiring arguments with someone with nothing happening, and sometimes they go completely mad when they even see something most mundane. Then they talk to themselves, see things that aren't there, stare into nothing, many disturbing things. Poleksija's words leave an effect on Rastko. A curse... Of course. A curse sent by the Satanic Catholic and Bogumil heretics! They must pay for ruining the lives of his sisters...
Later that day they raced to the logger's shed, in the most isolated corner of the property. Rastko found Doroteja unconscious in the woods, covered in the blood and innards of a rabbit she tried to eat alive. To this sight Isidora simply collapsed, and Vasilisa entered some sort of trance where she sat down on a stump and started mindlessly rocking back and forth.
Rastko's tutor, a mysterious Bulgarian monk Jovan agreed to Rastko's theory and insisted that's what happened. Rastko sworn that those responsible will feel his wrath and the wrath of God...
*******
Due to their insanity, the knowledge of which started to spread, the triplets would understandably be extremely unpopular as brides. Eventually, in 1385 Vasilisa would be married to none other than Jogaila, Grand Duke of Lithuania, and only with a massive dowry in gold. A year later Doroteja would be married to an Irish nobleman of all things. This made Isidora fall into a great sorrow, as she got scared that Poleksija's joke was prophetic in nature. But it was not to be - she would marry a Silesian Piast at the end of the 1386. They eventually learned to control their outbursts, but would forever remain on the edge of sanity. Jogaila merely married Vasilisa for political reasons, and because at the moment there weren't any more options that would result in anything meaningful. This way, he improves the relations with a powerful state, wins over his Orthodox subjects by converting, and gains an potential ally against Poland or the Tatars, and at last, but not the least, a pretty hefty sum of money made taking in the unfortunate woman palatable. All 3 however turned out to be very good wives and great patrons of culture, and even managed to predict and somewhat control their outbursts, though they always remained on the edge of sanity.
The last and final problem was the one in Asia Minor. Uroš needed to get rid of the troublesome territory, yet keep it as a buffer zone. He then decided to kill many birds with one stone - the area would be divided in 4 - Pontus, Paphlagonia, Bithynia and Ionia. These areas would be given to troublesome nobles, and the law was made very lax in them when it comes to privileges of the nobility. They would become states-within-state, and the most troublesome nobles would move there to be able to do what they want. But they would also be responsible for keeping the Turkish incursions in check. Uroš knew well that now that the land was theirs, they will be very responsible in keeping it safe. It worked like a charm - nobles flooded the area upon the implementation of the decision in 1389 and quickly fortified their holdings, and the area became much more civilized, even if basically independent.
*******
The ancient greatness of Constantinople seems to have evaporated after the Serbs and Bulgarians entered in 1364 and never returned. Almost half the city lays abandoned still - only the harbors are busy, and the villas and houses of the people now end up being turned into warehouses. Greeks can now seldom be seen - most of them left after they rioted and burned everything. Now a good chunk of the city are Genoan and Venetian quarters, and even they are half-abandoned - it's not that the merchants left, but that the new Emperor enlarged their concessions so much there simply aren't enough people to move in. They're the only ones to not be scraping by - the shipping never decreased, and now maybe even increased as the Asian coast has been brought to heel. Only the Hagia Sophia looks as good, no, even better than ever - renovated for the wedding of Prince Strahinja. But the city is now reduced to a collection of houses and ramshackle huts built in between and on top of them by God knows what peoples, surrounding the massive church.
Yet the worst of all are the cannon foundries and gunpowder mills built on the edges of the city, which means they were actually quite distant, an endless row of ruined houses lying between them and what the city was reduced to. In them workers endlessly toil to make armaments. The workers are mostly Albanians, with some Hungarians too. But the worst about it is that they test their creations right then and there, just shooting at abandoned houses until they collapse. A small field of debris surrounds the foundry, and the entire area is very disturbing to travelers - what has the Queen of Cities been reduced to?
These are probably the thoughts of a few of the remaining native Constantinopolitans - and truly, the city started acting basically as a mere giant stopping place for merchants who would take or leave goods from the endless storehouses, and then go on their merry way. There simply was no attempt to restore the city even a bit, and the cannon makers liked to test their creations on the houses indeed. It was basically a slum surrounded by ruin even in 1383. As a matter of fact, the biggest source of the Greek population were students at the Pandidakterion. It, along with the Hagia Sophia were the only remnants of old Byzantium. Maybe things would change in the future?
[1] - this word is today used by Croats for university, but no doubt that it would have been used at the time, especially due to the specific nature of it. Literally means "all-learning place"
[2] - the Pandidakterion was secular, but still operated by the church. However, Uroš, perhaps taking his father's separation of church and state (indeed, Dušan basically completely separated the two in his code, and even gave certain obligations to the chruch, such as mandatory feeding of the poor). This will have interesting effects in the future.
[3] - a strange artefact from the unusual process of the spread of literacy to the Slavs was the fact that the official language was this weird conlang designed to be understood by all Slavs, however it of course majorly eroded over time, and Dušan even had all his proclamations written in the vernacular instead. Due to this very thing is why Slavic languages have much cleaner orthographies than western languages - the standard language of culture was quite literally a foreign one, so when the time came to spread literacy to the masses linguists had to put in the work to have people learn how to write, and not literally learn a new language along it.
[4] - Novi Pazar
[5] - Kyustendil