Osman declared the independence of his own small kingdom from the Seljuk Turks in 1299. The westward drive of the Mongol invasions had pushed scores of Muslimstoward Osman's Anatolian principality, a power base that Osman was quick to consolidate. As the Byzantine Empiredeclined, the Ottoman Empire rose to take its place.

Founding an empire
Ertuğrul, Osman's father, led his Kayi tribe west into Anatolia, fleeing Mongol belligerence. Under the auspices of the Seljuks of Rum, he founded a town known as Sogut. This location was auspicious, as the wealthy Byzantine Empire was reeling in the West, and Muslim forces in the East were splintering under Mongol aggression. Baghdad had been sacked by Hulagu Khan in 1258, the very year Osman I was born.
Osman became chief, or Bey, upon Ertuğrul’s death in 1281. At this time, mercenaries streamed into his realm from all over the Islamic world to fight against and hopefully plunder the weakening Orthodox empire. Turkic numbers were constantly reinforced by a flood of refugees, fleeing from the Mongols. Of these, many were Ghazi warriors, or fighters for Islam, border fighters who believed they were fighting for the expansion or defense of Islam.

After the last prince of the family of Ala-ad-Din, to which Osman's family had been indebted for its foundation in Asia Minor, died, there was no other among the various emirs of that country who could compete with Osman for the headship of the whole Turkish population and dominion over the whole peninsula, save the Emir of Karamanogullari. A long and fierce struggle between the descendants of Osman and the Karamanogullari princes for the ascendancy commenced in Osman’s lifetime and was protracted during the reigns of many of his successors. Osman himself had gained some advantages over his Karamanli rival, but the rich yet vulnerable possessions of the Byzantine Emperor in the northeast of Asia Minor were more tempting marks for his ambition than the Karamanoglu plains, and it was over Greek cities and armies that the triumphs of the last 26 years of Osman’s life were achieved.

Turkic peoples called themselves Osmanli until the dissolution of the Ottoman Empire.
Potential rival
Osman’s uncle, the aged Dundar, who had marched with Ertugrul from the Euphrates 70 years before, was still alive when Osman, in 1299, summoned a council of his principal followers and announced to them his intention to attack the important Greek fortress Keaprihissar. His uncle opposed this enterprise, concerned that it would provoke the neighboring rulers, Turkish as well as Greek, to the detriment and possible destruction of Osman's tribe. Osman reportedly spoke not a word in reply but killed his old uncle on the spot, as a lesson to potential opponents.
Military victories

In 1301, after soundly defeating a Byzantine force near Nicea, Osman began settling his forces closer to Byzantine-controlled areas. Large numbers of Ghazi warriors, Islamic scholars, and dervishes began settling in Osman-controlled areas, and migrants composed the bulk of his army. The influx of Ghazi warriors and adventurers of differing backgrounds into these lands spurred subsequent Ottoman rulers to title themselves "Sultan of Ghazis" (Runciman 1990, p. 32).
Alarmed by Osman's growing influence, the Byzantines gradually fled the Anatolian countryside and dedicated their resources to the navy instead. Byzantine leadership was determined to prevent Osman from crossing into Europe and attempted to contain Ottoman expansion westward. Osman, however, continued to press westward and captured the Byzantine city of Ephesus near the Aegean Sea.


Further galvanized by the influx of migrants into his territory, Osman also moved eastward and seized Byzantine domains in the Black Sea region of Anatolia.
Osman's last campaign, before dying of old age, was against the Byzantines in the city of Bursa (Runciman 1990, p. 33). Although Osman did not physically participate in the battle, the victory at Bursa proved to be extremely vital for the Ottomans as the city served as a staging ground against the Byzantines in Constantinople, and as a newly adorned capital for Osman's son, Orhan.
Prophetic vision
Osman was 24 at the time of his accession, and had already proven his skills as both a leader and a warrior. His early fortunes and exploits are favorite subjects with Near Eastern writers, especially love stories of his wooing and winning the fair Mal Hatun. Ottoman writers attached great importance to these legends, characteristic of dynastic mythology in medieval and biblical chronicles.
There is a well-known story about a sleepless night Osman spent before taking the throne. One day, when he was 19 years old, his father Ertugrul went to visit a distant friend with his family, where they would remain overnight. The host of the house shows Osman his room and everyone retires for the night. Just after he prepares to go to sleep Osman notices the Qur'an hanging on the wall. His respect for the holy book of Islam keeps him from lying down, and as he is a visitor, he cannot take the Qur'an out of the room. He decides not to sleep until morning and sits beside the sofa. However, he is unable to stay awake and falls asleep for a short time just before dawn.

As he sleeps, he dreams he sees a crescent coming out of the chest of his mentor, Sheikh Edebali, and going into his body. Afterwards an enormous plane tree emerges from his chest and covers all the sky, shading the earth, the people enjoying and benefiting from his shade. He then wakes. When he and his family get back to their village, he recounts this dream to Sheikh Edebali, who smiles after hearing the dream and tells Osman that Allah would grant him and his descendants an enormous empire and he will receive the hand of Sheikh Edebali's daughter Mal Hatun in marriage. Because of his loyalty to Islam and his sharpness, courage, and generosity, he was nominated to be the ruler of the Kayi Clan.
Ottoman sources often dwell on the prophetic significance of Osman's name, which means "bone-breaker," signifying the powerful energy with which he and his followers showed in the following centuries of conquest. The name is also one given to a large species of vulture, commonly called the royal vulture, which is considered the emblem of sovereignty and warlike power in the East, comparable to the eagle in the nations of the West.
Osman's legacy
The Ottomans, one of a number of Turkic tribes in Asia Minor, were notable in that they were able to transform military victories into effective political administration. Osman was as much a soldier as an able administrator. Although motivated by religious zeal, and capable of ruthlessness towards his enemies, he expanded his realm through tolerance and cooperation with Greek Christians. They welcomed the order, stability, and security that Osman's rule brought in the face of a gradual breakdown in the central administration from Constantinople. Freed from Constantinople's onerous tax burden, and allowed to conduct their affairs largely free from interference, intermarriage between Greeks and Turks became common, and a large number of Christians eventually adopted the Muslim faith. This religious tolerance became the hallmark of Ottoman rule for the next 600 years.
In literature
Osman is celebrated by Near Eastern writers for his personal beauty, and for “his wondrous length and strength of arm.” Like Artaxerxes Longimanus of the old dynasty of Persian kings, Liu Bei in the Romance of the Three Kingdoms, Gautama the Buddha, and the Highland chieftain of whom Wordsworth sang, Osman is said to have been able to touch his knees with his hands when standing upright. He was claimed to be unsurpassed in his skill and graceful carriage as a horseman, and the jet black color of his hair, his beard, and eyebrows, gained him in youth the title of “Kara,” meaning “Black,” Osman. The epithet “Kara,” which is often found in Turkish history, is considered to imply the highest degree of manly beauty when applied to a person. He dressed simply, in the tradition of the first warriors of Islam, and like them, he wore a turban of ample white linen, wreathed round a red center. His loose flowing caftan was of one color, and had long open sleeves.

Sultans of the Ottoman Empire

Rise (1299–1453) Osman I - Orhan I - Murad I - Bayezid I - Mehmed I - Murad II - Mehmed II
Growth (1453–1683) Bayezid II - Selim I - Suleiman I - Selim II - Murad III - Mehmed III - Ahmed I - Mustafa I - Osman II - Murad IV - Ibrahim I - Mehmed IV
Stagnation (1683–1827) Suleiman II - Ahmed II - Mustafa II - Ahmed III - Mahmud I - Osman III - Mustafa III - Abdul Hamid I - Selim III - Mustafa IV - Mahmud II
Decline (1828–1908) Abdülmecid - Abdülâziz - Murad V - Abdul Hamid II

Dissolution (1908–1923) Mehmed V - Mehmed VI