Many people believe that Iraqi dictator Saddam Hussein decided to invade Iran for personal miscalculation based on ambition and a sense of vulnerability and insecurity. Saddam believed that over throwing the shah of Iran would give Iraq power over gulf and to regain control over the Shatt al Arab waterway. Even though Saddam had established and Iraqi nation-state, he feared that Iraq's new developed leadership [lead by Ayatollah Sayyid Ruhollah Musavi Khomeini] would threaten the Sunni-Shia [although the Shias constitute more then 50 percent of the population, they occupy a relatively insignificant number of government posts]. balance and would make the most of Iraq's minimal access to the Persian Gulf.
As late as mid 1979, Iraqi authorities invited Mehdi Bazargan [first Prime Minister of the Islamic Republic of Iran], to visit Iraq with the hope of improving relations between the two nations. Relations were strained when the Barzagan government came to it's ruins in late 1979 and Islamic militants vouching for a foreign policy that looked to achieve more economic and political power.
The spring of 1980 witnessed the events which officially wrecked relations. The Baath leadership feared that the success of Iran's Islamic Revolution would serve as an inspiration to Iraqi Shias. These fears escalated in July 1979, when riots broke out in An Najaf and in Karbala after the government had refused Ayatollah Muhammad Baqir as Sadr's request to lead a procession to Iran to congratulate Khomeini. Even more worrisome to the Baath was the discovery of a clandestine Shia group headed by religious leaders having ties to Iran. Baqir as Sadr was the inspirational leader of the group, named Ad Dawah al Islamiyah (the Islamic Call), commonly referred to as Ad Dawah. He espoused a program similar to Khomeini's, which called for a return to Islamic precepts of government and for social justice. In April the Iranian-supported Ad Dawah attempted to assassinate Iraqi foreign minister Tariq Aziz. Shortly after the failed grenade attack on Tariq Aziz, Ad Dawah was suspected of attempting to assassinate another Iraqi leader, Minister of Culture and Information Latif Nayyif Jasim.
Saddam Hussein officially abolished the 1975 treaty [1975 Algiers Agreement which was meant to settle disputes over the lands between Iraq and Iran: Shatt al-Arab and Khuzestan] by announcing that Shatt al Arab had returned to Iraqi control. Iran aggressively rejected this act and tensions escalated as both nations engaged in exchanging bombs deep within each other's territory. This was the beginning of what was soon to become a total war.
Iraq saw that Iran's Islamic revolution threatened their pan Arabism. The capital Baghdad became more confident, it saw the Iranian Army fall apart as some of it's highest and most competent officers were executed. In Khuzestan, the Iraqi intelligence were the first to stir up an uproar over labor disputes, and in the Kurdish area, another rebellion proved many troubles for the Khomeini government.
The Baathists were very confident as they planned out their military regime. This was because the Iranians lacked a structered and stable leadership. But more so, in reports made by Iraqi intelligence, the Iranians also lacked spare parts for their American-made equipment and that served as a very troublesome boundary for Iranians since they knew the lifespan of their equipment was limited. On the contrary, Iraq, more specifically Baghdad, were prepared with a fully equipped, armed, and trained mass of men. Iraqi's didn't feel the need to fear the Iranian forces especially the Pasdaran (Revolutionary Guards led by religious mullahs with no military experience). Saddam had assembled an army of 190,000 men, with 2,200 tanks and 450 aircrafts which were the epitome of soviet engineering in the market. They were equipped with Soviet river-crossing equipment making it easier for Iraqi men to cross the Shatt al Arab. The Iraqi army was made up of twelve divisions. At Khuzestan, the Iranian army which originally consisted of two divisions in that area became a number of battalion-sized formations.
The only thing that Iraqi's were worried about the Iranian air force which were utilizing some of the most sophisticated American-made aircrafts. The air force proved its strength in the many riots and demonstrations. The air force was also active in the failed United States attempt to rescue American hostages in 1980. This show force had impressed Iraqi decision makers and pushed them to decide on launching a major pre-emptive air strike on Iranian air bases in an effort simalar to the one that Israel using during the Arab-Israeli War.