Creation of the Il-Khanate
In 1255, Hulegu was appointed by his brother, Mongke, as the new governor of Persia. The following year his brother bestowed upon him the title of Il-Khan, meaning a subordinate Khan. Even though they would eventually gain complete independence, the Il-Khans would keep this seemingly demeaning title. In 1259, Mongke died. Hulegu played an important part in securing Kublai's victory their brother, Ariq Boke, and his allies in the Khanate of the Golden Horde. In return he received complete independence as Il-Khan.
War Against the Ummayad Caliphate
In 1258, Hulegu started a war against the now weak and crumbling Ummayad Caliphate. He sacked their capital at Hifez and destroyed most of Islam. It became a relgion worshipped by people in remote mountain villages in Iran, hiding from a world dominated by Buddhism.
War against the Byzantines
In 1260, Michael VIII of the Byzantine Empire attacked Mesopotamia in Hulegu's absence and heavily defeated the resident general, Kitbuqa. In 1261, he pushed on into Iran, only to be heavily defeated by a returning Hulegu at Shiraz. In 1262, Hulegu took the offensive against the Byzantines, capturing the Levant and cutting Egypt off from the rest of the empire. Only Antioch stood against him.
However, Hulegu was now in failing health and when Michael VIII came to him with a proposition for peace, Hulegu accepted on the condition that he kept the Levant for the Il-Khanate. In 1265, Hulegu died.