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.
Persian Corridor
Following Germany's invasion of the USSR in June 1941, Britain and the Soviet Union became allies. Britain and the USSR saw the newly opened Trans-Iranian Railway as an attractive route to transport supplies from the Persian Gulf to the Soviet Union. Britain and the USSR used concessions extracted in previous interventions to pressure Iran (and, in Britain's case, Iraq) into allowing the use of their territory for military and logistical purposes. Increased tensions with Britain led to pro-German rallies in Tehran. In August 1941, because Reza Shah refused to expel all German nationals and come down clearly on the Allied side, Britain and the USSR invaded Iran, arrested the monarch and sent him into exile to South Africa, taking control of Iran's communications and the coveted railway.