The Siege of Baghdad, which occurred in 1258, was an invasion, siege and sacking of the city of Baghdad, the capital of the Abbasid Caliphate at the time and the modern-day capital of Iraq, by the Ilkhanate Mongol forces along with other allied troops under Hulagu Khan. The main aim of Hulagu's expedition into the Middle East was to establish the firm imperial (now Toluid) control over the area and to extend the empire but not directly overthrow the Abbasids who had submitted to them previously. If the Abbasid Caliph only refused to submit and send a contingent, the Khagan ordered his brother, Hulagu, to destroy him.

The invasion left Baghdad in a state of total destruction. Estimates of the number of inhabitants massacred during the invasion range from 100,000 to 1,000,000. The city was sacked and burned. Even the libraries of Baghdad, including the House of Wisdom, were not safe from the attacks of the Ilkhanate forces, who totally destroyed the libraries and used the invaluable books to make a passage across Tigris River^{[citation needed]}. As a result, Baghdad remained depopulated and in ruins for several centuries, and the event is widely regarded as the end of the Islamic Golden Age.

Baghdad (Arabic: بغداد‎, Baġdād, IPA: [bæɣˈdæːd]) is the capital of Republic of Iraq, as well as the coterminous Baghdad Province. The population of Baghdad as of 2011 is approximately 7,216,040, making it the largest city in Iraq, the second largest city in the Arab World (after Cairo, Egypt), and the second largest city in Western Asia (after Tehran, Iran).

Located along the Tigris River, the city was founded in the 8th century and became the capital of the Abbasid Caliphate. Within a short time of its inception, Baghdad evolved into a significant cultural, commercial, and intellectual center for the Islamic World. This in addition to housing several key academic institutions (e.g. House of Wisdom) garnered the city a worldwide reputation as the "Center of Learning". Throughout the High Middle Ages, Baghdad was considered to be the largest city in the world with an estimated population of 1,200,000 people. The city was largely destroyed at the hands of the Mongol Empire in 1258, resulting in a decline that would linger through many centuries due to frequent plagues and multiple successive empires. With the recognition of Iraq as an independent state (formerly the British Mandate of Mesopotamia) in 1938, Baghdad gradually regained some of its former prominence as a significant center of Arabic culture.

Hulagu Khan, also known as Hülegü, Hulegu (Mongolian: Hülegü Khaan, "Warrior"; Mongolian Cyrillic: Хүлэг хаан; Turkish: Hülâgü Han; Chagatai/Urdu: ہلاکو Hulaku; Persian/Arabic: هولاكو خان‎; Chinese: 旭烈兀; c. 1217 – 8 February 1265), was a Mongol ruler who conquered much of Southwest Asia. Son of Tolui and the Kerait princess Sorghaghtani Beki, he was a grandson of Genghis Khan, and the brother of Arik Boke, Möngke Khan and Kublai Khan. Hulagu's army greatly expanded the southwestern portion of the Mongol Empire, founding the Ilkhanate of Persia, a precursor to the eventual Safavid dynasty, and then the modern state of Iran. Under Hulagu's leadership, the Mongols destroyed the greatest center of Islamic power, Baghdad, and also weakened Damascus, causing a shift of Islamic influence to the Mamluks in Cairo. During Hulagu's reign historians began writing in Persian instead of Arabic^{[citation needed]}.

Hulagu was born to Tolui, one of Genghis Khan's sons, and Sorghaghtani Beki, an influential Kerait princess. Sorghaghtani successfully navigated Mongol politics, arranging for all of her sons to become Mongol leaders. She was a Nestorian Christian, and Hulagu was friendly to Christianity. Hulagu's favorite wife, Dokuz Khatun, was also a Christian, as was his closest friend and general, Kitbuqa. It is recorded however that he was a Buddhist as he neared his death, against the will of Dokuz Khatun.

Osman I or Othman I or El-Gazi^{[citation needed]} (1258 – 1326) Ottoman Turkish: سلطان عثمان غازى Sultan Osman Ghazi, Turkish: Osman Gazi or Osman Bey or I. Osman, Osman Gazi Han), nicknamed "Kara" for his courage, was the leader of the Ottoman Turks, and the founder of the dynasty that established and ruled the Ottoman Empire. The Empire, named after him, would prevail as a world empire for over six centuries.

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

Ertuğrul, Osman's father, led the Turkic Kayi tribe west into Anatolia, fleeing the Mongol onslaught. His mother was named Khaima. He pledged allegiance to Sultan Kayqubad I of the Seljuk principality of Rum, who gave him permission to establish an emirate and expand it if he could, at the expense of the neighboring Byzantine provinces.