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.
Iran–Iraq relations
Since the Ottoman–Persian Wars of the 16th and 17th centuries, Iran (known as "Persia" prior to 1935) and the Ottomans fought over Iraq (then known as Mesopotamia) and full control of the Shatt al-Arab until the signing of the Treaty of Zuhab in 1639 which established the final borders between the two countries. The Shatt al-Arab was considered an important channel for both states' oil exports, and in 1937, Iran and the newly independent Iraq signed a treaty to settle the dispute. In the same year, Iran and Iraq both joined the Treaty of Saadabad, and relations between the two states remained good for decades afterwards.