Short answers, pulled from the story.
Osman I, a Turkoman chieftain operating in the Sakarya region of northwestern Anatolia, founded the Ottoman Empire in the year 1302. The empire emerged from a beylik, or principality, established by Osman I in northwestern Anatolia.
The walls of Constantinople fell to the cannons of Sultan Mehmed II on the 29th of May 1453. This event ended the thousand-year reign of the Byzantine Empire and marked the birth of a new global order.
The true decline of the Ottomans began when they suffered military defeats in the late 18th and early 19th centuries, culminating in the loss of territory and the rise of nationalism in the Balkans. The Crimean War of 1853 to 1856 forced the Ottoman state to issue foreign loans amounting to 5 million pounds sterling, leading to a financial crisis that culminated in the empire declaring bankruptcy in 1875.
Between 1821 and 1922, more than five million Muslims were driven from their lands, and five and one-half million Muslims died, some of them killed in wars, others perishing as refugees from starvation and disease. These migrations continued to our day, and the quantitative indicators cited in various sources show that during this period a total of about 7 million migrants from Crimea, the Caucasus, the Balkans, and the Mediterranean islands settled in Anatolia.
The sultanate was abolished on the 1st of November 1922, and the last sultan, Mehmed VI, left the country on the 17th of November 1922. The Republic of Turkey was established in its place on the 29th of October 1923, in the new capital city of Ankara.