When the Treaty of Sèvres allowed European powers to divvy up the Ottoman Empire, they drew borders for new modern countries. When they created a new country in what had been part of the Sassanian Empire in ancient Mesopotamia, they named it Iraq. Iraq comes from an Arabic name for the area. It may relate to the ancient city of Uruk. Iraq’s neighbor, Iran, got its name through other channels.
Modern Iran was not under Ottoman control, but ruled by the Pahlavi dynasty. Reza Shah Pahlavi (15 March 1878 – 26 July 1944) gave the name Iran to his country in 1935. The country had been called Eransahr during the ancient Persian Sassanian Empire and the people whom we would call Iranians, were then called Eran, according to my reading of Encyclopedia Iranica’s article “ĒRĀN, ĒRĀNŠAHR“. Furthermore, the root word appears to be Er, which is cognate with the word Aryan — of the people speaking Aryan languages. Although Eransahr was the formal name for the kingdom of the Eran, the term Eran was used instead of Eransahr early on.
The list of areas that spoke the language of the Eran includes
Pārs Persis, Pahlaw Parthia, Xūzestān Susianē, Mēšān Mesēnē, Asūrestān Assyria, Nōdšīragān Adiabēnē, Ādurbāyagān Atropatēnē, Spāhān (Isfahan), Ray Rhages, Kirmān Karmania, Sagestān Sakastanē, Gurgān Hyrkania, Marw Margianē, Harēw Areia, Abaršahr (Khorasan), Tūrestān Turēnē, Makurān (Makran), and Kūšānšahr tā frāz ō Paškabūr the Kushan country up to Peshawar, Māy Mēdia, Hind India, and “on that side of the sea” Mazūnšahr (Oman), and others, namely Arman Armenia, Wiruzān Iberia (Georgia), Alān Albania, and Balāsagān tā frāz ō Kāf kōf ud Alānān dar Balasagan up to the Caucasus and the Gate of the Alans,
again, according to the Iranian Encyclopedia article’s list, which is based on inscriptions at at Naqš-e Rostam and Sar Mašhad. Those not in Eransahr — the Roman Empire and the lands of the Caucasus — were anērānšahr.
Ghodrat-Dizaji says what is meant by Aneran and Eran is specified in inscriptions, Pahlavi books, and in Persian and Arabic writings, with the Caucasus and Armenia as part of Eran under Shapur I, but not according to a leading priest of the early Sassanian period, and under Narses (293-302 AD), when Eran was south of Armenia. For the Zoroastrian priest, Kirder, those in the group of Anuran were not only non-Iranian linguistically but also those who worshipped demons.
The Greeks and Romans preferred to refer to the Iranians by terms related to smaller geographic and tribal units. μηδισμός, medismos or “medize” is a term used around the time of the Greco-Persian Wars by the Greeks to refer to people who sympathized with the (formerly dominant) Medes.
(Herodotus Book 7 132.1 says “Among those who paid that tribute [to the Persians] were the Thessalians, Dolopes, Enienes, Perrhaebians, Locrians, Magnesians, Melians, Achaeans of Phthia, Thebans, and all the Boeotians except the men of Thespiae and Plateau.”)
Persia was a term related to the (then) dominant group and so the name was given to the whole.
Pars was an area of Iran; the language of Pars, Parsi. When the Arabs took control, they changed the P to a related phoneme in their language, giving the name Farsi to the language of the Persians. The Persian language was in danger of being lost to Arabic when the Samanid dynasty (819-999) came to power. During their tenure, Iran experienced a golden age for arts and science. Avicenna is probably the most famous of the scholars they attracted. It was under the Samanids that the poet Ferdowsi wrote his Persian language Shahnameh (Book of Kings), a monumental epic that helped boost the status of the language.
I am sorry, but I have yet to be convinced about how all the tribal and place words Pars, Parthia, and Parni connect with the name Persia. See Parthia.
Persia or Iran, Persian or Farsi
Ehsan Yarshater; IRANIAN STUDIES, VOL. XXII, No.1, 1989
Ghodrat-Dizaji, Mehrdad. “ADMINISTRATIVE GEOGRAPHY OF THE EARLY SASANIAN PERIOD: THE CASE OF ĀDURBĀDAGĀN.” Iran 45 (2007): 87-93.
More on what Herodotus has to say about the Persian peoples:
“61. Now those who served were as follows:–The Persians with this equipment:–about their heads they had soft felt caps called tiaras, and about their body tunics of various colours with sleeves, presenting the appearance of iron scales like those of a fish, and about the legs trousers; and instead of the ordinary shields they had shields of wicker-work, under which hung quivers; and they had short spears and large bows and arrows of reed, and moreover daggers hanging by the right thigh from the girdle: and they acknowledged as their commander Otanes the father of Amestris the wife of Xerxes. Now these were called by the Hellenes in ancient time Kephenes; by themselves however and by their neighbours they were called Artaians: but when Perseus, the son of Danae and Zeus, came to Kepheus the son of Belos and took to wife his daughter Andromeda, there was born to them a son to whom he gave the name Perses, and this son he left behind there, for it chanced that Kepheus had no male offspring: after him therefore this race was named.”
“62. The Medes served in the expedition equipped in precisely the same manner; for this equipment is in fact Median and not Persian: and the Medes acknowledged as their commander Tigranes an Achaimenid. These in ancient time used to be generally called Arians; but when Medea the Colchian came from Athens to these Arians, they also changed their name. Thus the Medes themselves report about themselves. The Kissians served with equipment in other respects like that of the Persians, but instead of the felt caps they wore fillets: and of the Kissians Anaphes the son of Otanes was commander. The Hyrcanians were armed like the Persians, acknowledging as their leader Megapanos, the same who after these events became governor of Babylon.”