List of ancient great powers
The Sassanid Empire is the name used for the fourth Iranian dynasty, and the second Persian Empire (226–651). The empire's territory encompassed all of today's Iran, Iraq, Armenia, Afghanistan, eastern parts of Turkey, and parts of Syria, Pakistan, and large parts of Caucasia, Central Asia and Arabia. During Khosrow II's rule in 590–628 Egypt, Jordan, Palestine, Lebanon were also briefly annexed to the Empire, as well as far west as western Asia Minor. The Sassanid era, encompassing the length of the Late Antiquity period, is considered to be one of the most important and influential historical periods in Iran. In many ways the Sassanid period witnessed the highest achievement of Persian civilization. The empire is furthermore known for being the arch-rival of the neighboring Roman–Byzantine Empire for a period of over 400 years. As the Parthians were replaced by the Sassanids, they carried on the already century long lasting Roman–Persian Wars, which would eventually become the longest conflict in human history.
Iranian nationalism
Iran regained its political unity and was given a new distinct religious identity under the Safavids. Shia became the official state religion and henceforth played an important role in the reconstruction of a new ethno-religious identity for the Iranian people. Furthermore, the rise of the Safavid empire coincided with the rise of the neighbouring Ottoman empire in West Asia and North Africa (and most importantly, for centuries Iran's geo-political as well as ideological arch rival), the Mughal empire in India, and the Uzbek empire in Central Asia, all adhering to Sunni Islam. The formation of these political entities helped create a distinct Iranian-Shia political identity among these polities. It also helped to expand the hegemony of Persian language in much of the Islamic world. Persian literature was, apart from Iran and its territories stretching from the North Caucasus to the Persian Gulf, produced from Anatolia to Central Asia and the Indian subcontinent.