Rum-Seljuks (Chaos)

Until the seperation
Originally just one breakaway part of the Turkish Seljuk tribe (there were also the, the and the ) in Anatolia, on the former territory of Byzantium, the Rum-Seljuks later formed one of the greatest empires in the. In OTL they were destroyed by the in 1243 (which allowed the Ottomans to get their own country, and later become an empire themselves), which didn't happen here. Sultan continued to reign until 1259.

1225, they had conquered as OTL, which was the start of their interfering in OTL Ukraine. They also made a peace treaty with the empire of in 1245; but since they weren't threatened by Mongols, ITTL they could demand tribute from Nikaia. Soon after this, they'd clash the first time with their great opponent, the Shahdom of, which had put under its protection in 1262.

1265, the Rum-Seljuks attacked Nikaia, threatened its capital. This time they were still content to get some areas (i.e. not the whole empire). But in 1284, they'd attack the resurrected again, and conquered Brussa, Nicomedia and Nikaia. (IOTL the Ottomans took eleven years for that, but they were one of many little princedoms in Anatolia then. The Rum-Seljuks, OTOH, already owned most of Anatolia...) 1292, the west of was conquered by the Rum-Seljuks.

While Constantinople may still have held out, the Rum-Seljuks were lucky when in 1302 the ambitious wanted to become new Latin Emperor. Thrace was overrun by Catholic mercenaries, and in their panic the Byzantines called the Seljuks for help. The Seljuks indeed threw the crusaders out again, but they didn't think about giving Thrace to Byzantium back either... 1304, the Kingdom of Lesser Armenia became a tributary of the Rum-Seljuks, even without war.

Once having entered the Balcans, the Seljuks went on to dominate it. In 1310, they defeated the first time, taking the South with Philippopolis (Plovdiv) and the Aegean coast. Czar fell in battle. 1314, was conquered by Seljuks; 1319, the disputed area of ; 1327 even Constantinople fell after a long siege, effectively defeated by the hunger. The East Roman Empire had ended.

1329, the Seljuks won another victory against Bulgaria. Sofia fell to their hands. 1333, they conquered. The remaining states in started to panic, appealed for a new crusade, but with no success: Italy was divided, the HRE kings struggled with the pope or were too weak,  was at the beginning too poor and later under various kings,  busy with Serbs and. Only in 1338, after the necessary organizations, a small crusade was organized mostly by small nations like, and Thessalia was reconquered. Bulgaria got Sofia back.

But the Seljuks went on: 1342, Lesser Armenia was annexed by the Rum-Seljuk Empire; 1347, they defeated the army of and, conquered the southern half of.

Separation and unification
In 1348, Rum-Seljuk sultan died and divided his empire between his sons  of Rum (who ruled the European possessions and about a quarter of Asia Minor) and  in Konya (former Ikonion).