Note: The beginnings of this TL were originally posted (in modified form)
here.
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POD: Instead of being his OTL self (prone to anger and fits of rage, excessively violent, may have been brain damaged)
Tsar Kaloyan of Bulgaria is a stable, well adjusted individual with a gift for diplomacy (along with his OTL military talents). Like OTL, he pursues an aggressive strategy toward Byzantium pre-1204, but thats because he dreams of making himself Emperor. Because of this and because he's a somewhat religious Orthodox Christian, he doesn't enter a union with the Catholic church in 1202 like OTL.
April 30th, 1204. Tarnovo, Bulgaria.
"The Franks...you say they took Constantinople?" asked Ivan Kaloyan, Tsar of Bulgaria. Indeed, everyone in the throne room was staring openmouthed-the City had never fallen to an outsider before. And now, here was the messenger from the south, saying it had been done by an army that, until about a month ago, everyone in Bulgaria had thought was going to Egypt. People sat, taking in the news.
"Yes, stormed it, sacked it. You would not believe the stories I've heard-they looted the city, the Imperial palace, even the churches"-at this, Ivan Kaloyan's mouth turned down. He might have fought against Constantinople, but he was also known for his piety. "Yes, even the churches. They desecrated the Hagia Sophia! They had a drunk, naked harlot dancing on the Holy Alter!"
"What, what-How dare they? HOW DARE THEY!! GODS HOLY CHURCH!" No one present, ever, could remember seeing Ivan Kaloyan this mad, his face red, his fist shaking. It was some time before his courtiers calmed him down, and his rage went to a managable level. It was still there, but he could make plans. He talked with his generals, with his diplomats, with his nobles, and he made plans. He would use this situation to his advantage, come closer to the throne of Constantinople. As a young man, he'd been a diplomatic hostage in the City, laid eyes on that throne, and vowed to sit on it, if at all possible. Thinking about the events of the last month, it seemed ever more possible. And those Franks were going to be sorry they'd ever so much as touched Hagia Sophia.
-April 14th, 1205. Bulgarians win the Battle of Adrianople against the Latin Empire, killing over 300 crusader knights and several thousand infantry, and taking only light casualties. Latin Emperor Baldwin is captured, sent to Tarnovo, and executed (OTL)
-1206: Bulgarian forces ravage Thrace, but fail to take Adrianople.
-1207: Bulgarians kill Boniface, Latin King of Thessalonica, at the battle of Messinopolis. (OTL) A Bulgarian attempt to siege the city fails, and so the Bulgarians launch an offensive into Latin-held Thessaly.
Ivan Kaloyan takes great pains to emphasize his public piety, and officially portrays his war against the Latin Empire as the struggles of a religious man to liberate his fellow Orthodox Christians from rule by heretics. As far as possible, he treats both the ex-Byzantine population and aristocracy well, provided that they remain loyal to him*[OTL Kaloyan behaved quite differently]. Most are quite happy to do this, preferring to be ruled by Kaloyan rather than the heretical Franks.
Later in 1207, Kaloyan signs an alliance against the Latin Empire with Theodore Laskaris, ruler of the Empire of Nicea, a breakaway state formed after the fall of Constantinople. As a condition of this, he agrees to marry his son Peter to Irene, Theodore Laskaris' daughter.
1207-1218: Kaloyan conducts a series of offensives throughout Thessely and Macedonia, gradually consolidating Bulgaria's hold over those territories and reducing the Kingdom of Thessalonica to just its capital city and the immediate environs. Nicea is somewhat less successful, loosing much of the Asia minor coastline to the Latins.
1210: Epirus tries to conquer some of Thessalonica's southern possessions. Bulgaria goes to war with them, and Epirus looses the Battle of Larissa, ending its ambitions for the moment.
1219: Thessalonica falls to the Bulgarian siege. Ivan Kaloyan orders his court to relocate there (it being, by far, the largest and wealthiest city in his domains). The confiscated estates of Latin nobles are awarded to members of the Bulgarian aristocracy, who are settled around the city. (Thus separating them from their power bases in Bulgaria proper). Greek becomes the court language, and a number of Byzantine aristocrats are given positions in the government. Ivan Kaloyan begins refferring to himself as "Emperor and Autocrat of the Bulgarians and Romans".
1224: The Empire of Nicea wins the Battle of Poemanenum against the Latins, and subsequently pushes them out of Asia Minor (except for the eastern shore of the Bosphorus, which the Latins still hold)
1225: Kaloyan dies. His son Peter is occupied having to fight his uncle Ivan, who rallies an army in northern Bulgaria and claims the throne. The newly incoporated Greek aristocrats and the Bulgarians around Thessalonica support Peter, but it will be three years before Ivan's army is finally defeated.
1226-1228: During the chaos surrounding the Bulgarian succession war, Epirus occupies large parts of Macedonia.
1228-1233: Peter launches an offensive into Epirus, recovering most of Macedonia. Epirus is ultimately forced to cede the nortern half of its domains, including Albania.
1234: Encouraged by the Pope, Hungary declares war on Bulgaria. Bulgaria is defeated at the Battle of Severin in 1235 and forced to cede all its possessions north of the Danube.
1237: Bulgaria declares war on the Latin Empire, now reduced to just Thrace. Bulgaria invades with an army of almost 30,000 men, drawn from all over its territories, and virtually wipes out a much smaller Latin army at the Second Battle of Adrianople. Adrianople itself is taken after a three month siege, and the Bulgarian army criss-crosses Thrace. Gallipoli surrenders in 1238, and by 1240, the "Latin Empire" has been reduced to about a ten-mile radius around Constantinople. The treasury begins to run dangerously low, and many of the Frankish nobles still left choose to leave the City for the Italian-held Greek islands, or even their ancestral homes in France or Germany.
1241: Hungarians suffer a massive defeat by the Mongols, allowing Peter to recover Wallachia. The Mongol victory sends tens of thousands of Cumans-who fleeing the Mongols, had initially sought refuge in Hungary-into Bulgaria. The Bulgarians offer all the Cumans a home in exchange for their agreeing to convert to Orthodoxy, swear loyalty to the Bulgarian/Roman empire, and provide military service. Many of the Cumans are settled along the Anatolian frontier to guard against the Turkish Beyliks, and Cuman horse archers become an integral part of the Bulgarian/Byzantine military.
1243: Thanks to Kaloyan, Bulgaria had a small navy, founded after the fall of Thessalonica and now consisting of seventeen war galleys plus transports. However, institutions are harder to build than ships, and even by number of boats, Peter's navy is still rather pathetic compared to either Venice or Genoa. For his further plans, Peter is going to need a much stronger seafaring force than he has. So he concludes an alliance with Genoa, promising them duty-free trade in his domains, the right to build trading colonies in Thessalonica and Constantinople (should the latter fall into Peter's possession), support in any war Genoa wages with a foreign power, and a fifty year lease on the island of Thasos.
1243: Mongols win the Battle of Kopat Dag against the Rum Seljuks, sending the latter into a terminal decline. Peter marries a Bulgarian princes off to the Mongols, and Trebizond becomes a vassal.
1244: With naval support from the Genoese, Peter declares war on Nicaea, claiming its throne in right of his wife Irene and young son Ivan (or Ioannes). A Bulgarian/Greek army crosses the Dardenelles (some on Genoese ships), and, in a three-year campaign, conquers the Nicaean "Empire". More Bulgarians (especially those thought to support the rebellion of 1225-28) are settled in newly conquered Thrace and Anatolia.
1246: Hungary invades and again retakes Wallachia, forcing Bulgaria to recognize the Danube as the Bulgarian-Hungarian border. This will remain for several decades.
1247: Peter dies, and his son is crowned as Ivan (or Ioannes), Emperor and Autocrat of the Bulgarians and Romans.
1248: Again with Genoese naval support, Ioannes declares war on Latin Constantinople. Even with mercenaries hired by Latin Emperor Henry II, the walls are severely undermanned. The Latin treasury is dry, and defeatism is rampant.
June, 16th, 1248. Ioannes, Emperor and Autocrat of the Bulgarians and Romans, rubbed the sleep out of his eyes and groggily got up and left his tent. It was night, the stars were out, and the view was dotted with watchfires set by sentries, all along the siege lines that stretched from the Golden Horn to the Sea of Marmara. Less than a mile away was Constantinople. City of Emperors, long mistress of the Bosphorus, protected by massive walls that still seemed invincible as ever. "What is it that was worth waking me up for?" asked Ioannes.
"Our sentries caught this man here, walking to the lines from the City. Calls himself Demetrios, says he's from a mercenary company guarding the Saint Romanus Gate, and that his employers have a nice deal they could offer us. He doesn't have any weapons on him, we've checked."
"Well, why would I?" said a voice, as a short, rather oily man stepped into view. "I mean, that miser in the Emperor's palace hasn't paid us in two months, and everyone knows he's got no money too. You see, none of us like working for free, and we don't intend to do it any longer. We thought you might be able to offer us a better deal. The right amount of gold, you know...and it might get quite difficult for us to remember to keep that gate closed."
"I think," said Ioannes, "that there might be something to your offer."
Demetrios was sent back towards the walls with some gold. The sentries followed, and watched as two more mercenaries raised him back over the walls. He'd been promised more if, the next day, his company did indeed "forget" to close the gate.
The next day, the Greco-Bulgarians launched an assault on the city. The first wave hit the northern end of the wall in the morning, and about an hour later, while the Latins were distracted, another group of several thousand men made their way towards the Saint Romanus gate. Obligingly, it opened. "Don't you guys know you're supposed to keep people like us out?" laughed the Greek commander Grigorios. Demetrios walked out. "Coin, you know, can be so bad for the memory sometimes."
Ionnes entered Constantinople that evening. The Latins had finally been banished from the city of the Patriarchate, and, in an elaborate ceremony, Ioannes is re-crowned in Roman style in Constantinople as Ioannes III, with his title reversed to "Emperor and Autocrat of the Romans and Bulgarians". Ioannes proclaims the grand "restoration" of the Roman Empire from rule by Latin heretics.
1250-1256: Ioannes leads further campaigns in the southern Balkans. Epirus, Athens, and the Pelleponese are all conquered.
1257: Greeks around Thrace and Anatolia, angered by the settlement of Bulgarians and Cumans and that the Roman Empire is being ruled by "barbarians", rebel and proclaim Androkinos Palaiologos, member of a well-established Byzantine noble family and relative of the pre-1204 Angeloi dynasty, Emperor. The rebellion conquers much of the Thracian and Anatolian countryside, but fails to take any major cities and is put down in the spring of 1257, with much assistance from the Cumans. Androkinos and sixteen other leaders of the rebellion are executed, and many of the supporters are made to settle in Bulgaria.
1258: Hulegu Khan sacks Baghdad and burns down the famed "House of Wisdom". Much of the city's population is killed.
1260: Hulegu is defeated by the Egyptian Mamluks at the Battle of Ayn Jalut
1264: Nogai Khan, a Mongol general in the Golden Horde, raids Bulgaria but is bought off with a tribute of fabrics and gold, and another Byzantine princess.