The Beylik of Osman was formed in 1299 by Turkish mercenaries immigrating to central Anatolia, in the employ of many of the feudal Muslim nations in Anatolia. By mid-1300, it had invaded the north of Byzantine holdings in Anatolia, taking a wide swath of land that included Heraclea. However, Byzantine forces pushed back, and Osman forces retreated to their own territory, and agreed to a peace treaty. After that, dealings with the Byzantine Empire were very peaceful.
In the summer of 1301, Goynuk was invaded to further Osman Bey's ambitions. Their army was caught completely by surprise, and a third of the country was lost before the forces could regroup. Goynuk surrendered, ceding a wide swath of land, and agreeing to pay tribute to Osman. However, Goynuk instigated a revolt inside Osman territory in 1303, leading to its subsequent complete annexation. However, this annexation led to the Border War with Germiyan and Karesi.
Post-War Osman-Byzantine Relations
After the war with the Roman Empire, relations improved to the point that the Byzantine Emperor, Andronikos IV, ceded a large amount of land, including Herculaneum, to the Beylik. This led to increased opening of trade and relations, and in 1306, a formal military alliance was agreed on.
Early in 1305, Osman Bey completely abolished the feudal system, bringing all lands directly under his control. This allowed for more dynamic military campaigning, and for a larger and more professional army to be raised. However, it also sowed the seeds of many of the Goynuk rebellions, which were instigated in many cases by disenfanchised nobles.
Early Osman Imperial Ambitions
In autumn, 1305, 7,500 troops invaded Bulgaria. Though it was hoped that the encroaching winter would forestall any counterattack, the Bulgarians instead used it to their advantage, hiding in the heavy snow and generally letting the heat-loving Anatolian troops freeze their toes off (in many cases, literally. Frostbite was a massive claimer of digits in the Bulgarian War). Though it was arduous work, a small strip of land was finally captured, and immediately given to the Byzantine Empire to help cement their new alliance.
The Border War
As Osman forces made their way across the Beylik of Goynuk, letters for aid were dispatched to Germiyan and Karesi. Both wasted no time in invading, having been waiting for years for an excuse to annihilate this upstartBeylik. Inconclusive fighting see-sawed back and forth across the border, for years, neither side gaining the upper hand. Karesi had no real military to speak of in comparison to the Beylik of Osman's professional army, and the Beylik of Germiyan's army was in the west, fighting the Byzantine Empire. However, the Beylik of Osman's army was tired and bloody from years of multiple-front fighting, and so could not invade, even when given the chance.