(CNN)On Thursday the US Army War College published a monumental and authoritative history of the Iraq War. One of its sober conclusions: "An emboldened and expansionist Iran appears to be the only victor" of the Iraq War.

Under the Iraqi dictator Saddam Hussein, Iran and Iraq had waged an almost decade-long war of attrition during the 1980s. With Saddam deposed as a result of the US invasion of Iraq in 2003, Iran has since expanded its influence not only into Iraq but also into Syria and Yemen.

Too often, US military histories focus only on tactical issues that are unmoored from deeper political questions, which of course misses the point; as Clausewitz famously observed, "War is the continuation of politics by other means."

The Army's history of the Iraq War, while focusing on the Army's operations, also takes into account the many political factors in Washington and on the ground in Iraq that affected the course of the war, and it also takes to task American political and military leaders for errors that they made during the conflict.

The essential message of the Iraq War history is that wishful thinking and ignorance were the key drivers of the early decision-making about the conflict.

The history was commissioned by then-Army Chief of Staff Gen. Raymond Odierno in 2013. Odierno told Army historians that it was necessary to write a real history of the Iraq War because the Army had never done one for the Vietnam War, and had spent the first few years of the Iraq conflict relearning costly lessons from that conflict.

To inform the Iraq War history, the Army declassified 30,000 pages of documents related to the conflict.

Army historians also performed more than 100 interviews with key players such as President George W. Bush. (Disclosure: I was one of the peer reviewers for the manuscript and also know the two historians who led the project, now-retired Army Cols. Joel Rayburn and Frank Sobchak.)

The Army's history is likely to be the most authoritative account of the Iraq War by any American institution. Unlike in the United Kingdom, where there was the seven-year Chilcot Inquiry into the British role in the Iraq War, hitherto there has been no official American investigation into the conduct of the most lethal and costly conflict that the United States has fought since Vietnam.

Devastating portrait of Rumsfeld

The Iraq War history is a reminder that President Bush committed the United States to a costly and counterproductive war, the planning for which began only two months after the 9/11 attacks. According to the history, Secretary of Defense Donald Rumsfeld asked war planners at the Pentagon for plans for the overthrow of Saddam Hussein's regime on November 27, 2001. This was before the defeat of the Taliban in Afghanistan had even been completed and al Qaeda was still fighting American soldiers on the ground there.

The history paints a devastating portrait of Rumsfeld, the only Bush administration official who refused to do an interview with the Army historians. Rumsfeld kept pushing for a smaller number of troops for the initial invasion of Iraq and also the subsequent occupation of the country. As a result, the war was always under-resourced in terms of the number of troops on the ground necessary "to defeat both the Sunni insurgency (including al Qaeda in Iraq) and the Iranian-backed Shia militants simultaneously," according to the history.

Another problem was that the United States knew very little about Iraq. The history points out that there were "gaping holes in what the US military knew about Iraq. This ignorance included Iraqi politics, society, and government -- gaps that led the United States to make some deeply flawed assumptions about how the war was likely to unfold."

One of those flawed assumptions was that the Pentagon believed the Iraqis would greet the US military as liberators just as they had been in France when they liberated the country from the Nazis at the end of World War II. It didn't, of course, turn out that way.

Some of the greatest blunders

The Iraq War study also helps shed considerable light on two of the greatest blunders of the conflict, which were the first two orders of the Coalition Provisional Authority (CPA) that oversaw the US occupation of Iraq. The first order was to fire between 30,000 and 50,000 leading members of the Baathist party and the second was to dissolve the Iraqi army.

Those orders helped set the stage for the subsequent insurgency, since hundreds of thousands of Iraqi soldiers were suddenly out on the street without a job and the large-scale firing of the Baathists left the country without many capable administrators who had joined the party simply because it was a requirement for their jobs.

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On May 9, 2003, Rumsfeld ordered Paul "Jerry" Bremer, who led the CPA, to "actively oppose" organizations loyal to Saddam Hussein, and the Pentagon drafted an order to remove anyone from office who was in the top four levels of the Baath party. Ten days later, Bremer sent a memo to Rumsfeld recommending the dissolution of the Iraqi army.

Toward the end of May, Bremer announced the de-Baathification order and dissolved all the units of the Iraqi military. President Bush told the Army historians that the order dissolving the Iraqi military surprised him, but the Iraqi army had effectively disbanded already, and Bremer was closer to the situation on the ground than he was.

Then-Brig. Gen. Mark Hertling, now a CNN contributor, received the news about the dissolution of the Iraqi army when he was in the middle of addressing 600 senior Iraqi military officers that he was trying to recruit to participate in the reconstitution of the Iraqi army, according to the history.

These early CPA decisions "effectively collapsed the edifice of the Iraqi state, creating a national governance and security vacuum that would take another six to seven years to refill. When combined with abortive reconstruction efforts and unmet popular expectations, these factors became major contributors to Iraq's gradual descent into full insurgency and civil war," according to the history.

The Army history is far from entirely critical, pointing to areas of innovation, such as the early adoption of counterinsurgency tactics by some Army units and the reconciliation efforts with Sunni tribes that once had fought the American military but were eventfully put on the US payroll.

Other innovations included the use of commanders' funds to sustain local projects and the creation of highly effective medical evacuation systems that resulted in a much higher survival rate for the wounded than was the case in previous conflicts.

A new approach in early 2007

When it became clear that the United States was losing the Iraq War in early 2007, a new approach and a new commander were installed by the Bush administration. The new approach was deploying counterinsurgency tactics with a larger American force on the ground that was led by Gen. David Petraeus. Petraeus positioned many of his forces to live among the population rather than on massive bases insulated from the Iraqi people as had previously been the case. This generated more intelligence about the insurgents and also helped to tamp down the sectarian conflicts in Iraq.

This approach finally turned the conflict around so that the violence began to abate dramatically in Iraq. Insurgent attacks went down from a high of 140 a day, so that by the end of 2008 "the coalition routinely experienced days with no attacks at all throughout the entire country," according to the history.

The Iraq War history ends with the pullout of all US troops in 2011, so it doesn't recount the rise of ISIS in Iraq three years later, which itself was a product of the American decision to invade Iraq in 2003. As a result of that invasion, al Qaeda, which had had no presence in Iraq under Saddam, formed Al Qaeda in Iraq, which is the parent organization of ISIS.

This is all an expensive lesson in hubris for the United States. As the Army history recounts, "Nearly 4,500 American military personnel lost their lives in the fighting, and another 32,000 were wounded -- many of them grievously. More than 300 soldiers from other coalition nations also perished. Estimates on Iraqi casualties vary wildly, ranging from roughly 200,000 killed to more than a million.

"Monetary costs, for the United States only, are similarly hard to approximate due to the challenge in estimating future costs for veterans' care and the interest on loans taken out to finance the war. There is no question that the war has been expensive, ranging even among the lower estimates from a cost of over 800 billion to nearly 2 trillion dollars."

Hopefully the Army history will teach future generations of military and political leaders what pitfalls can be avoided the next time the United States decides to fight a complex insurgency war.