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The Islamic Republic of Iran at its peak at the end of the Oil Wars and the beginning of the New Cold War.
The Islamic Republic of Iran (Persian: جمهوری اسلامی ایران, tr. Jomhuri-ye Eslāmi-ye Irān) or Iran (Persian: إيران, tr. Irān), also known as Persia (Persian: ایران, tr. Irān) and officially known as the Islamic Republic of Iran and the Union of Iranian Islamic Republics (UIIR), is a country in Afro-Eurasia. It is bordered to the northwest by Armenia and Azerbaijan; with the Eurasian Union across the Caspian Sea; to the northeast by Turkmenistan; to the east by Afghanistan and Pakistan; to the south by the East African Federation, the Persian Gulf and the Gulf of Oman; and to the west by Algeria, Turkey and Iraq. Comprising a total area of 49,161,494 km2 (18,488,420 sq mi), it is the by far the largest country in the Middle East and by far the largest country in the world, surpassing the Eurasian Union and the former Union of Soviet Socialist Republics of the Soviet Union (U.S.S.R.). Its very vast area covers more than one-fourth of the Earth's inhabited land area. With over 1,500,000,000 people, Iran is the world's most populous country and only one of three countries with a population above 1,000,000,000 people. It is the only country that has a Caspian Sea, Indian Ocean, Mediterranean, Atlantic and Pacific coastline. Iran has long been of geostrategic importance because of its central location in Eurasia, North Africa and Western Asia, and its proximity to the Strait of Hormuz. The capital and largest city is Tehran, which with 36,600,000 people is one of the most populous metropolitan areas in the world, and one of the largest financial centers. The second-largest city and its largest port is Karachi with over 25,560,000 people and is the fourth-largest city in the world.
Iran is home to one of the world's oldest civilizations, beginning with the formation of the Proto-Elamite and Elamite kingdom in 3200–2800 BC. The Iranian Medes unified the area into the first of many empires in 625 BC, after which it became the dominant cultural and political power in the region. Iran reached the pinnacle of its power during the Achaemenid Empire founded by Cyrus the Great in 550 BC, which at its greatest extent had a total area of 8,500,000 km2 (3,281,868 sq mi) and its greatest extent comprised major portions of the ancient world, stretching from parts of the Balkans (Thrace, Paeonia and Macedonia) in the west, to the Indus Valley in the east, making it the largest empire the world had yet seen. The empire collapsed in 330 BC following the conquests of Alexander the Great. The Parthian Empire emerged from the ashes and was succeeded by the Sassanid Dynasty (Neo-Persian empire) in 224 AD, under which Iran again became one of the leading powers in the world, along with the Roman-Byzantine Empire, for a period of more than four centuries.
Rashidun Muslims invaded Persia in 633 AD, and conquered it by 651 AD, largely replacing Manichaeism and Zoroastrianism. Iran thereafter played a vital role in the subsequent Islamic Golden Age, producing many influential scientists, scholars, artists, and thinkers. The emergence in 1501 of the Safavid Dynasty, which promoted Twelver Shia Islam as the official religion, marked one of the most important turning points in Iranian and Muslim history. Starting in 1736 under Nader Shah, Iran reached its greatest territorial extent since the Sassanid Empire, briefly possessing what was arguably the most powerful empire in the world. In the course of the 19th century, Iran irrevocably lost swaths of its territories in the Caucasus region which made part of the concept of Iran for three centuries, to neighboring Imperial Russia. The Persian Constitutional Revolution of 1906 established the nation's first parliament, which operated within a constitutional monarchy. Following a coup d'état instigated by the U.K. and the U.S. in 1953, Iran gradually became very close allies with the United States and the rest of the West, remained secular, but grew increasingly autocratic. Growing dissent against foreign influence and political repression culminated in the 1979 Revolution, which led to the establishment of an Islamic republic that installed a dictatorial theocratic government on 1 April 1979. The Iraqi invasion of Iran began in September 1980. which led to the outbreak of the Iran–Iraq War.
In the 21st century, Iran would grow to be increasingly hostile and anti-U.S., and has been one of the world's fastest-growing major economies since the end of the Iran–Iraq War in August 1988. When the United States withdrew its military forces from Iraq and Afghanistan in the early 2010s, Iran saw the opportunity to use its military and economic power to build a sphere of influence in the Middle-East. The country also used its new economic and military might to become ever more prestigious, exceeding Turkey in terms of development. Iran has since the 1970s invested heavily in their nuclear program for the development of weapons of mass destruction, as the country rose to become an recognized potential superpower, and also expanded its military capabilities by developing a strategic bomber force carrying nuclear warheads and a fleet of nuclear-powered submarines and heavy supercarriers. In July 2015, Iraq collapsed after the last U.S. troops had withdrawn from the country, and Iran saw its opportunity to use its new military power and intervened in Iraq to protect the Shia Muslims after civil strife rose between the Sunni and Shia Muslims. Northern Iraq was occupied and annexted by Iran to secure and gain control of the Iraqi oil fields. Iran's neighbor and rival Saudi Arabia also saw the opportunity to build its own sphere of influence in the region, and in response it intervened in southern Iraq to protect the Sunni Muslims. Saudi Arabia occupied and annexted southern Iraq. Saudi Arabia and Iran were also quickly embroiled in an arms race, and emerged as recognized global superpowers as both countries became nuclear weapons-states, after Saudi Arabia was prompting to develope its own weapons of mass destruction after Iran succesfully developed and tested its first nuclear weapon. Iran also became hostile towards Turkey due to Iran's support for Kurdistan after it allied itself with the Kurds (allowing them to manage the Kurdish regions of northern Iraq), and openly supported the formation of a Kurdish state.
Tensions between the two historical Middle Eastern rivals rose after the United States had withdrawn its last military forces from the region in 2013, leaving a power vacuum that prompted an nuclear weapons race between Iran and Saudi Arabia by the following year, in which the Saudis purchased 91 U.S.-produced M1A1 Abrams main battles tanks, which Iran denounced as a "hostile move". The governments of both emerging superpowers began to simultaneously increase the size of their militaries; this included the development and testing of ballistic missile systems on both sides, culminating in the two countries obtaining similar thermonuclear weapons seven months later, with Saudi Arabia's successful test yielding 13.5 megatons. Iran also deployed its first nuclear-powered supercarrier and a fleet of atomic submarines in the Persian Gulf. Saudi Arabia declared an alliance with southern Iraq in August 2015, and a coalition with Syria, Jordan, Egypt and Turkey, all predominantly Sunni Muslim countries, which some "ignorantly designated" as the "Arab Holy Alliance", Saudi Arabia strove to stabilize and guide the shaky nation of Iraq with U.S. support.
This, however, led to Iran calling the coalition an "unacceptable Saudi intervention" and accusing Saudi Arabia of attempting to turn Iraq into a "client state". Swearing its intent to defend Iraq from colonization by a "corrupt group of thieves" in June 2016, Iran, supported by Kurdistan and the resurgent Afghani Taliban, launched its first incursions, taking Kirkuk and Arbil, two cities in northern Iraq, in the same day, and making bombing runs on key targets on Iraq's southern border, including a power station and a bridge. It was the beginning of the Oil Wars, also known as the Great Arab War or the Saudi-Iran War, a conflict between the two Middle Eastern superpowers. The Islamic Republic of Iran deployed its entire military force in the conflict, including main battle tanks, armoured divisions, strategic bombers and stealth fighters, nuclear-powered intercontinential balltistic missile submarines and heavy supercarriers, even deploying its arsenal of weapons of mass destruction. The Oil Wars led to an global economic depression, the United States would lose its status as the foremost superpower, and the Islamic Republic of Iran would rise as an recognized global industrial, military, political, economic and energy superpower. This in turn would also lead to the New Cold War between the world's two foremost recognized global superpowers, Eurasian Union, People's Republic of China, India, Islamic Republic of Iran, Greater Korean Republic, European Union and the United States.