Median kingdom in the context of "Persia"

The Achaemenid Empire (/əˈkiːmənɪd/ ə-KEE-mə-nid; Old Persian: 𐎧𐏁𐏂, Xšāça, lit. 'The Empire' or 'The Kingdom') was an ancient Iranian empire founded by Cyrus the Great of the Achaemenid dynasty in 550 BC. At peak, its territorial extent was roughly 5.5 million square kilometres (2.1 million square miles), making it the largest empire of its time. Based in the Iranian plateau, it stretched from the Balkans and Egypt in the west to the Indus Valley in the east, including Anatolia, Cyprus, Mesopotamia, the Levant, parts of Eastern Arabia, and large parts of Central Asia.

By the 7th century BC, the region of Persis, located in the southwestern part of the Iranian plateau, had been settled by Persians. From Persis, Cyrus rose and defeated Media, Lydia, and the Neo-Babylonian Empire, thus marking the establishment of a new imperial polity in the ancient Near East. While its conquests were largely successful in most regions, the Achaemenid Empire's attempts to expand into Greece proved extremely difficult over the course of decades of wars and multiple kings, ultimately resulting in its defeat in the Greek mainland.

Iran, officially the Islamic Republic of Iran and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the northeast, Afghanistan to the east, Pakistan to the southeast, and the Gulf of Oman and the Persian Gulf to the south. With a population of over 90 million, Iran ranks 17th globally in both geographic size and population and is the sixth-largest country in Asia. Iran is divided into five regions with 31 provinces. Tehran is the nation's capital, largest city, and financial center.

Home to one of the world's oldest continuous major civilizations, most of Iran was first united as a nation by the Medes under Cyaxares in the 7th century BC and reached its territorial height in the 6th century BC, when Cyrus the Great founded the Achaemenid Empire. Alexander the Great conquered the empire in the 4th century BC. An Iranian rebellion in the 3rd century BC established the Parthian Empire, which later liberated the country. In the 3rd century CE, the Parthians were succeeded by the Sasanian Empire, who oversaw a golden age in the history of Iranian civilization. During this period, ancient Iran saw some of the earliest developments of writing, agriculture, urbanization, religion, and administration. Once a center for Zoroastrianism, the 7th century CE Muslim conquest brought about the Islamization of Iran. Innovations in literature, philosophy, mathematics, medicine, astronomy and art were renewed during the Islamic Golden Age and Iranian Intermezzo, a period during which Iranian Muslim dynasties ended Arab rule and revived the Persian language. This era was followed by Seljuk and Khwarazmian rule, Mongol conquests and the Timurid Renaissance from the 11th to 14th centuries.

The History of Iran (also known as Persia) is intertwined with Greater Iran, which is a region encompassing all of the areas that have witnessed significant settlement or influence by the Iranian peoples and the Iranian languages – chiefly the Persians and the Persian language. Central to this region is the Iranian plateau, now largely covered by modern Iran. The most pronounced impact of Iranian history can be seen stretching from Anatolia in the west to the Indus Valley in the east, including the Levant, Mesopotamia, the Caucasus, and parts of Central Asia. It also overlaps or mingles with the histories of many other major civilizations, such as India, China, Greece, Rome, and Egypt.

Iran is home to one of the world's oldest continuous major civilizations, with historical and urban settlements dating back to the 5th millennium BC. The Iranian plateau's western regions integrated into the rest of the ancient Near East with the Elamites (in Ilam and Khuzestan), the Kassites (in Kuhdesht), the Gutians (in Luristan), and later with other peoples like the Urartians (in Oshnavieh and Sardasht) near Lake Urmia and the Mannaeans (in Piranshahr, Saqqez and Bukan) in Kurdistan. German philosopher Georg Wilhelm Friedrich Hegel called the Persians the "first Historical People" in his Lectures on the Philosophy of World History. The sustained Iranian empire is understood to have begun with the rise of the Medes during the Iron Age, when Iran was unified as a nation under the Median kingdom in the 7th century BC. By 550 BC, the Medes were sidelined by the conquests of Cyrus the Great, who brought the Persians to power with the establishment of the Achaemenid Empire. Cyrus' ensuing campaigns enabled the Persian realm's expansion across most of West Asia and much of Central Asia, and his successors would eventually conquer parts of Southeast Europe and North Africa to preside over the largest empire the world had yet seen. In the 4th century BC, the Achaemenid Empire was conquered by the Macedonian Empire of Alexander the Great, whose death led to the establishment of the Seleucid Empire over the bulk of former Achaemenid territory. In the following century, Greek rule of the Iranian plateau came to an end with the rise of the Parthian Empire, which also conquered large parts of the Seleucids' Anatolian, Mesopotamian, and Central Asian holdings. While the Parthians were succeeded by the Sasanian Empire in the 2nd century, Iran remained a leading power for the next millennium, although the majority of this period was marked by the Roman–Persian Wars.