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After the Iranian Revolution

Tensions between Iraq and Iran were fuelled by Iran's Islamic revolution and its appearance of being a Pan-Islamic force, in contrast to Iraq's Arab nationalism. Despite Iraq's goal of regaining the Shatt al-Arab, the Iraqi government initially seemed to welcome the Iranian Revolution, which overthrew Shah Mohammad Reza Pahlavi, who was seen as a common enemy. There were frequent clashes along the Iran–Iraq border throughout 1980, with Iraq publicly complaining of at least 544 incidents and Iran citing at least 797 violations of its border and airspace.

Ayatollah Ruhollah Khomeini called on Iraqis to overthrow the Ba'ath government, which was received with considerable anger in Baghdad. On 17 July 1979, despite Khomeini's call, Saddam gave a speech praising the Iranian Revolution and called for an Iraqi-Iranian friendship based on non-interference in each other's internal affairs. When Khomeini rejected Saddam's overture by calling for Islamic revolution in Iraq, Saddam was alarmed. Iran's new Islamic administration was regarded in Baghdad as an irrational, existential threat to the Ba'ath government, especially because the Ba'ath party, having a secular nature, discriminated against and posed a threat to the fundamentalist Shia movement in Iraq, whose clerics were Iran's allies within Iraq and whom Khomeini saw as oppressed.

Saddam's primary interest in war may have also stemmed from his desire to right the supposed "wrong" of the Algiers Agreement, in addition to finally achieving his desire of becoming the regional superpower. Saddam's goal was to supplant Egypt as the "leader of the Arab world" and to achieve hegemony over the Persian Gulf. He saw Iran's increased weakness due to revolution, sanctions, and international isolation. Saddam had invested heavily in Iraq's military since his defeat against Iran in 1975, buying large amounts of weaponry from the Soviet Union and France. Between 1973 and 1980 alone, Iraq purchased an estimated 1,600 tanks and APCs and over 200 Soviet-made aircraft.

By 1980, Iraq possessed 242,000 soldiers, second only to Egypt in the Arab world, 2,350 tanks and 340 combat aircraft. Watching the disintegration of the powerful Iranian army that frustrated him in 1974–1975, he saw an opportunity to attack, using the threat of Islamic Revolution as a pretext. Iraqi military intelligence reported in July 1980 that despite Iran's bellicose rhetoric, "it is clear that, at present, Iran has no power to launch wide offensive operations against Iraq, or to defend on a large scale." Days before the Iraqi invasion and in the midst of rapidly escalating cross-border skirmishes, Iraqi military intelligence again reiterated on 14 September that "the enemy deployment organization does not indicate hostile intentions and appears to be taking on a more defensive mode."

Some scholars writing prior to the opening of formerly classified Iraqi archives, such as Alistair Finlan, argued that Saddam was drawn into a conflict with Iran due to the border clashes and Iranian meddling in Iraqi domestic affairs. Finlan stated in 2003 that the Iraqi invasion was meant to be a limited operation in order to send a political message to the Iranians to keep out of Iraqi domestic affairs, whereas Kevin M. Woods and Williamson Murray stated in 2014 that the balance of evidence suggests Saddam was seeking "a convenient excuse for war" in 1980.

On 8 March 1980, Iran announced it was withdrawing its ambassador from Iraq, downgraded its diplomatic ties to the charge d'affaires level, and demanded that Iraq do the same. The following day, Iraq declared Iran's ambassador persona non grata, and demanded his withdrawal from Iraq by 15 March.