Iran has a long history, with the earliest settlers being Aryans around 1500 BC. The Persian Empire dominated the region for centuries until being conquered by Alexander the Great. Modern Iran was shaped by dynasties like the Qajars and Pahlavis; Reza Shah sought to modernize the country in the early 20th century. However, his son Mohammad Reza Shah grew increasingly authoritarian, facing opposition until the 1979 Islamic Revolution overthrew the monarchy and established an Islamic republic led by Ayatollah Khomeini.