Before we head straight into this question, a common misconception with the Iran-Iraq war is that neither parties had the intention of "overthrowing" the opposing government because it would be a near impossible task. The close economic, social and religious relationship between these two countries for the past few decades illustrates the few differences can only keep them fighting can only last for so long. Iraqi Shiites represents one of the biggest minorities outside of Iran (different sources say around 40% to 60% of the total population). The differences that existed between Iran and Iraq were territorial and political disputes, which aggravated after the Iranian Islamic Revolution in 1979. Even in the western NATO narrative of the war was to keep the region "stable" from one nation dominating the other as well as a fear of increased Soviet influence.^1 This was used to justify U.S. involvement in the war by supplying Iraq and Iran at the same time (Iran-Contra). Unfortunately, the end of the war found the two sides in roughly the same position as when the war started, with two important exceptions: Saddam Hussein's Iraq was armed to the teeth and facing a real economic problem as a result of the war; and the U.S. had by the end of the war become more directly involved militarily in the region than at any previous time.^2
To analyze this question, we would need to look at the events that led up to this war and Saddam's goals in fighting the Islamic Republic. The territorial disputes between Iran and Iraq has existed since the 19th century. In 1975, a major turning point in regional relations occurred when Iraq and Iran reached an agreement on all their outstanding differences. The Algiers Agreement, signed on March 1975, led Iraq to recognize Iranian sovereignty over half of the Shatt al-Arab river, a longstanding Iranian demand. In return, Iran agreed to turn over Iraq disputed territory along their central frontier and more importantly, to end its support for the Iraqi Kurdish rebellion. The dispute over the Shatt al-Arab would reemerge at the outset of the Iran-Iraq war in 1980. The importance of this river was imperative to both Iran and Iraq, economically and militarily. The river was Iraq's only outlet to the Persian Gulf. This agreement also gave Iran sovereign rights of access to the to the port of Abadan, where the Anglo-Iranian Oil Company had built an enormous oil refinery.^3
While border disputes was an important part of the Algiers Agreement, a more fundamental agreement was for each to accept the legitimacy and durability of the other's domestic regime. Since the Ba'thist takeover in 1968, both countries tried to foment domestic and political problems for the other; the prime example of Mohammad Reza Shah's support for Iraq's Kurdish opposition, and even go so far as sending Iranian troops to join the Kurdish side in early 1975.^4 The Ba'thist government definitely made the greater territorial compromise in ceding the Shatt al-Arab river, in return for breathing room for consolidating its hold over the country.
From the set of circumstances leading to the Iran-Iraq War, the Iranian Islamic Revolution had the biggest deciding factor in terms of regional power dynamics. Saddam saw the Revolution as a chance to take on Iran while it is in disarray, a power vacuum created by the Revolution that Iraq could easily exploit. However a more important factor was the threat posed by the revolution. The very fact that a mass-based, Islamist social revolution had occurred in the neighborhood was an implicit threat to the Ba'thist regime and the monarchical Arab states.^5
As Gregory Gauss (Professor of International Affairs and Head of the International Affairs Department at Texas A&M University) argues, the Iranian Revolution challenged the regional political stability of the Arab nations, which inevitably led to a direct military confrontation. Rather than fighting for an occupation or replacement of the Iranian regime from Saddam's perspective, the conflicts between Iran and its neighbors were about regional power, defining legitimate domestic political regimes. We see this idea of legitimacy through diplomacy in the Algiers Agreement and later legitimacy through military conflicts in the Iran-Iraq war. Despite Saddam's record of poor decision making, he knew that the overthrow of the Islamic Republic would take more than a border invasion as his own experience in the Ba'athist coups required years and decades of internal struggle. The war was a show of strength that ended up being a miscalculation behalf of Saddam.^6
Endnotes:
A great example is the United States' "Twin Pillar" strategy. See also Henry Kissinger. Years of Upheaval. Boston: Little, Brown. 1982. Pg 854-71.
F. Gregory Gause III. The International Relations of the Persian Gulf. Cambridge University Press. 2010. Pg. 37,46.
Richard Schofield. Evolution of the Shatt al-Arab Boundary Dispute. Wisbech, U.K,: Menas Press. 1986; and Khadduri. The Gulf War. Pg 35-41.
The Iranian support for Kurdish forces in Iraq tied much of the Iraqi army down in confronting the rebellion. Saddam Hussein later said in 1974 that Iraq suffered 60,000 casualties (dead and wounded) in the fighting. Kenneth M. Pollack. Arabs At War: Military Effectiveness, 1948-1991. Lincoln: University of Nebraska Press. 2002. Pg. 179
F. Gregory Gause III. Iraq's Decisions to Go to War, 1980 and 1990. Middle East Journal, Vol. 56, No. 1. Winter 2002. Pg 47-70.
F. Gregory Gause III. The International Relations of the Persian Gulf. Pg 61.
Edit: Spelling and Grammar.