Question: What is the name of the geographical region that early Islamic usage often regarded everywhere east of western Persia and where Vistaham helped Khosrow regain his throne after the rebellion of Bahram Chobin?  

full_context: Document 1: Greater Khorasan: Khorasan (Middle Persian: , Persian: خراسان‎ ‎ "Xorâsân"    ) is a historical region lying in the northeast of Persia. However, in pre-Islamic and early Islamic times, the term "Khurassan" frequently had a much wider denotation, covering also parts of Central Asia and Afghanistan; early Islamic usage often regarded everywhere east of western Persia, so-called Jibal or what was subsequently termed 'Irak 'Adjami, as being included in a vast and ill-defined region of Khurasan, which might even extend to the Indus Valley and Sind.
Document 2: Vinduyih: Vinduyih (Middle Persian: "Windôē") or Bendoy (New Persian) was a Sasanian nobleman from the Ispahbudhan family. His sister was the mother Khosrau II, thus making Vinduyih the uncle of Khosrau. Vinduyih and Vistahm played an important role in restoring the throne for Khosrau II from Bahram Chobin. He was later deposed in Ctesiphon by the orders of Khosrau II.
Document 3: Kashmir: Kashmir is the northernmost geographical region of the Indian subcontinent. Until the mid-19th century, the term "Kashmir" denoted only the Kashmir Valley between the Great Himalayas and the Pir Panjal Range. Today, it denotes a larger area that includes the Indian-administered territory of Jammu and Kashmir (subdivided into Jammu, Kashmir, and Ladakh divisions), the Pakistani-administered territories of Azad Kashmir and Gilgit-Baltistan, and Chinese-administered territories of Aksai Chin and the Trans-Karakoram Tract.
Document 4: Pashtunistan: Pashtūnistān (Pashto: پښتونستان‎ ; also transliterated Pakhtūnistān; lit. "homeland of the Pashtuns") is the geographic region inhabited by the indigenous Pashtun people of modern-day Afghanistan and Pakistan, wherein Pashtun culture, language, and national identity have been based. Alternative names historically used for the region included ""Afghānistān"" and ""Pashtūnkhwā"", since at least the 3rd century CE onward. Pashtunistan borders Punjab to the east, Persian and Turkic speaking regions to the west and north, Kashmir to the northeast, and Balochistan to the south.
Document 5: Sarames the Elder: Sarames the Elder was an Iranian officer of Median origin, who served in high offices under the Sasanian king Hormizd IV (r. 579–590), possibly as the governor of a province. When Bahram Chobin rebelled against Hormizd IV, Sarames was sent to suppress his rebellion, but was defeated and captured by the latter, who had him trampled to death by elephants.
Document 6: Hindu and Buddhist heritage of Afghanistan: Before the Islamic conquest of Afghanistan communities of various religious and ethnic background lived in the land. South of the Hindu Kush was ruled by the Zunbil and Kabul Shahi rulers. When the Chinese travellers (Faxian, Song Yun, Xuanzang, Wang-hiuon-tso, Huan-Tchao, and Wou-Kong) visited Afghanistan between 399 and 751 AD, they mentioned that Buddhism was practiced in different areas between the Amu Darya (Oxus River) in the north and the Indus River in the south. The land was ruled by the Kushans followed by the Hephthalites during these visits. It is reported that the Hephthalites were fervent followers of medieval Hinduism, and that they worshipped Hindu aspects of God, known as Shiva and Vishnu, as well as Surya.
Document 7: Vistahm: Bistam or Vistahm (also transliterated Wistaxm, Persian: بیستام‎ ‎ ), was a Parthian dynast of the Ispahbudhan house, and maternal uncle of the Sasanian "shah" of Persia, Khosrow II (reigned 591–628). Vistahm helped Khosrow regain his throne after the rebellion of Bahram Chobin, but later led a revolt himself, which encompassed the entire Iranian East before being suppressed.
Document 8: The Stolen Throne: The Stolen Throne is a fantasy novel written by Harry Turtledove and set in the Videssos universe. It is the first book in the "Time of Troubles" tetralogy. The events depicted are strongly based on the historical interaction of Sassanid Persia and Byzantium in the 6th and 7th century. The first book depicts the rise of Sharbaraz (the analog to Khosrau II) to overcome the usurper Smerdis (Bahram Chobin) to become the King of Kings of Makuran (Persia) with the help of the Videssian Emperor Likinios (Maurice).
Document 9: Shirin: Shirin (? – 628 AD) (Persian: شيرين‎ ‎ ) was a wife of the Sassanid Persian Shahanshah (king of kings), Khosrow Parviz. In the revolution after the death of Khosrow's father Hormizd IV, the General Bahram Chobin took power over the Persian empire. Shirin fled with Khosrow to Syria, where they lived under the protection of Byzantine emperor Maurice. In 591, Khosrow returned to Persia to take control of the empire and Shirin was made queen. She used her new influence to support the Christian minority in Iran, but the political situation demanded that she do so discreetly. Initially she belonged to the Church of the East, the so-called Nestorians, but later she joined the miaphysite church of Antioch, now known as the Syriac Orthodox Church. After conquering Jerusalem in 614, amidst the Byzantine–Sasanian War of 602–628, the Persians captured the True Cross of Jesus and brought it to their capital Ctesiphon, where Shirin took the cross in her palace.
Document 10: History of Kashmir: The history of Kashmir is intertwined with the history of the broader Indian subcontinent and the surrounding regions, comprising the areas of Central Asia, South Asia and East Asia. Historically, Kashmir referred to the Kashmir Valley. Today, it denotes a larger area that includes the Indian-administered state of Jammu and Kashmir (which consists of Jammu, the Kashmir Valley, and Ladakh), the Pakistan-administered territories of Azad Kashmir and Gilgit–Baltistan, and the Chinese-administered regions of Aksai Chin and the Trans-Karakoram Tract.
Document 11: Syria (region): The historic region of Syria (Hieroglyphic Luwian: "Sura/i"; ; in modern literature called Greater Syria, Syria-Palestine, or the Levant) is an area located east of the Mediterranean sea. The oldest attestation of the name Syria is from the 8th century BC in a bilingual inscription in Hieroglyphic Luwian and Phoenician. In this inscription the Luwian word "Sura/i" was translated to Phoenician "ʔšr" "Assyria." For Herodotus in the 5th century BC, Syria extended as far north as the Halys river and as far south as Arabia and Egypt. For Pliny the Elder and Pomponius Mela, Syria covered the entire Fertile Crescent. In Late Antiquity Syria meant a region located to the East of the Mediterranean Sea, West of the Euphrates River, North of the Arabian Desert and South of the Taurus Mountains, thereby including modern Syria, Lebanon, Jordan, Israel, the State of Palestine and parts of Southern Turkey namely the Hatay Province and the Western half of the Southeastern Anatolia Region. This late definition is equivalent to the region known in Classical Arabic by the name "ash-Shām " الشام /ʔaʃ-ʃaːm/ , which means "the north [country]" (from the root "šʔm " شأم "left, north"). After the Islamic conquest of Byzantine Syria in the 7th century AD, the name "Syria" fell out of primary use in the region itself, being superseded by the Arabic equivalent "Shām", but survived in its original sense in Byzantine and Western European usage, and in Syriac Christian literature. In the 19th century the name Syria was revived in its modem Arabic form to denote the whole of Bilad al-Sham, either as "Suriyah" or the modern form "Suriyya", which eventually replaced the Arabic name of Bilad al-Sham. After World War I, the name Syria was applied to the French Mandate for Syria and the Lebanon and the contemporaneous but short-lived Arab Kingdom of Syria.
Document 12: Narses (general under Maurice): Narses was a Byzantine general of Armenian ancestry active during the reigns of the emperors Maurice and Phocas in the late sixth and early seventh centuries. He commanded the army in Mesopotamia under Maurice. Together with Khosrow II, he fought against the Sasanian usurper Bahram Chobin. When Phocas overthrew Maurice and seized the throne, Narses refused to recognize the usurper. Besieged by Phocas' troops in the city of Edessa, Narses called for Khosrau to aid him and was rescued by the Persian forces. He attempted to salvage the situation with a diplomatic mission but was burned alive in Constantinople by Phocas' government after having been promised safety.
Document 13: Arachosia: Arachosia is the Hellenized name of an ancient satrapy in the eastern part of the Achaemenid, Seleucid, Parthian, Greco-Bactrian, and Indo-Scythian empires. Arachosia was centred on the Arghandab valley in modern-day southern Afghanistan, although its influence extended east to as far as the Indus River in modern-day Pakistan. The main river of Arachosia was called "Arachōtós", now known as the Arghandab River, a tributary of the Helmand River. The Greek term "Arachosia" corresponds to the Aryan land of "Harauti" which was around modern-day Helmand. The Arachosian capital or metropolis was called Alexandria Arachosia or Alexandropolis and lay in what is today Kandahar in Afghanistan. Arachosia was a part of the region of ancient Ariana.
Document 14: Mardansina: Mardansina (also spelled Mardan Sina) was a Parthian nobleman from the House of Mihran—he was the son of Bahram Gushnasp and thus the brother of the prominent Sasanian military leader Bahram Chobin, who managed to overthrow the Sasanian king himself briefly in 590–591, but was eventually defeated and killed. Mardansina thereafter became the new leader of the rebel movement of Bahram Chobin, and later took part in the rebellion of Vistahm (591–596 or 594/5–600).
Document 15: Persian language: Persian ( or ), also known by its endonym Farsi (فارسی "fārsi " ] ) or Parsi (پارسی "Pārsi "), is one of the Western Iranian languages within the Indo-Iranian branch of the Indo-European language family. It is primarily spoken in Iran, Afghanistan (officially known as "Dari" since 1958), and Tajikistan (officially known as "Tajiki" since the Soviet era), and some other regions which historically were Persianate societies and considered part of Greater Iran. It is written in the Persian alphabet, a modified variant of the Arabic script.
ground_truth: Khorasan