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.
Military history of Iran
The reigns of both Mohammad Shah and Nasser al-Din Shah also saw attempts by Persia to bring the city of Herat, occupied by the Afghans, again under Persian rule. In this, though the Afghans were no match for the Persian Army, the Persians were not successful, this time because of British Intervention as part of The Great Game "(See papers by Waibel and Esandari Qajar within the Qajar Studies source)". Russia backed the Persian attacks, using Persia as a 'cat's paw' for expansion of its own interests. Britain feared the seizure of Herat would leave a route to attack India controlled by a power friendly to Russia, and threatened Persia with closure of the trade of the Persian Gulf. When Persia abandoned its designs on Herat, the British no longer felt India was threatened. This, combined with growing Persian fears about Russian designs on their own country, led to the later period of Anglo-Persian military co-operation.