The origins of the Ottoman Empire are to be found in a combination of Turkish asabiyah and the Islamic spirit of ghazza (meaning, struggle in the cause of God). Asabiyah, a term used by Ibn Khaldun to denote tribal cohesion, is the force that holds together tribes through bonds of blood, a characteristic found in abundance among peoples of the desert and the nomads of the steppes. The Turks were a people who lived in the upper reaches of Central Asia, on the borders between Sinkiang Mongolia and Kazakhstan and possessed the qualities of asabiyah in abundance. They were, like their Mongol cousins, a people who roamed the grasslands on their horses, setting down their tents just long enough for rest and recuperation. They were known for their fierce loyalty to the clan and for their bravery and horsemanship.

In the 8th, century, as Islam spread towards the Amu Darya, the Turks came into contact with its universal precepts and embraced the new faith. Many found service in the armed forces of the Abbasid Empire. Using their innate qualities of leadership, some rose through the ranks, occupied important positions in the army and by the middle of the 9th century, became the kingmakers in Baghdad. By the end of the 9th century, they had replaced the Caliphate in Baghdad with the Sultanate as the de-facto political power. The rise of the Seljuks in the 11th century marked a high point in Turkish power. The Seljuk victory over the Byzantines in August 1072 was a turning point in world history and opened Anatolia to Turkish penetration. Until the advent of Hulagu Khan and the fall of Baghdad (1258), Turkish pressure on Byzantine holdings in Anatolia was continuous and forceful. There was a pause during the Mongol eruptions. Hulagu captured the upper reaches of the Rivers Tigris and Euphrates located in eastern Anatolia and forced the Turks further west. Most of Anatolia accepted Mongol dominance and the Mongol lords appointed their own satraps to rule over the local principalities.

But the Turks were not a people to accept Mongol over-lordship for long. After the Battle of Ayn Jalut (1261), Mongol power waned, while Turkish power gathered momentum. As early as the 11th century, the Turks were organized into effective brigades, each one led by a bey. The primary purpose of these brigades was to march against the Byzantine territories. It is here that the Islamic spirit of ghazza came into play.

Without Islam, the Turks were a roving band of nomads, not unlike the nomads of bygone eras, who were pushing against the frontiers of settled civilizations. With Islam, they became not just conquerors but founders of a global empire and a global civilization. The narrow asabiyah of tribe and race gave way to the global vision of Islam. Those who took part in ghazza were called ghazis. The term ghazi carries a connotation of valor, strength, humility, selflessness, charity, steadfastness, struggle and chivalry to this day in languages spoken by Muslims worldwide. There were several groups of ghazis and a person could move freely from one group to another.

It was these ghazis who cemented Turkish power in West Asia and projected it into the very heart of Europe. Uthman Ghazi emerged from among these ghazis as the bey (Turkish, meaning authority, leader) of the western marches. The house of Uthman is called Uthmanali and the empire founded by him is referred to as the Uthmania or Ottoman Empire. It is said that Uthmanali was inducted as a ghazi by a sage, Shaykh Ede Bali. By 1301, he controlled the swath of territory extending from Eskishehir to Bursa and advanced towards the old Byzantine capital of Iznik. Alarmed, the Byzantine Emperor sent a force under Muzalon to relieve Iznik. The Turks annihilated this force at the Battle of Yalakova (1301). This critical victory was a turning point for the Ottomans. Uthman’s fame spread far and wide in the Muslim world and attracted a growing number of volunteers for the ghazza.

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https://historyofislam.com/?s=it+eschewed+the+principles+of+tolerance+and

http://consult.islamstory.com/en/artical/20569/Origins-Ottoman-Empire-1