The Ottoman empire is named after Osman(d.1324), the eponymous founder of the dynasty, whose name came to be rendered in English as Ottoman. Osman was a Turkish frontier lord – beg in Turkish – who commanded a band of semi-nomadic fighters at the beginning of the fourteenth century in northwestern Asia Minor (Anatolia), known at the time to Turks, Persians, and Arabs as the land of Rum (Rome); that is, the land of the Eastern Roman Empire. Osman Beg was but one of many Turkish lords who carved out their respective principalities in western and central Asia Minor, profiting from the power vacuum caused by the Mongols’ destruction of the Seljuq sultanate of Rum in 1243.

The Fourth Crusade (1199–1204), culminating in the sack of Constantinople and the conquest of most of the Byzantine empire, is a textbook example of a noble plan gone awry. The original intent was to attack the Ayyubids in Egypt, but along the way financial and other considerations diverted the French and Venetian crusaders to Constantinople where they restored the deposed emperor Isaac II Angelos (r.1185–95, 1203–4) to power. According to an earlier agreement, Isaac was to provide the crusaders with military and financial aid, but fiscal problems within the empire made this impossible. As time passed, anti-Latin sentiment within the city led to a palace coup which overthrew Isaac. The crusaders then seized the city and the empire itself. The Fourth Crusade and the subsequent Latin conquest intensified the anarchy that already existed within the provinces, providing the grace blow to an empire which had become increasingly fragmented to the point of disintegration.