After many years of waiting, the Army has finally published its official history of the Iraq War. The authors of the two-volume history are retired Colonels Joe Rayburn and Frank Sobchak. Their comprehensive study, which amounts to around 1,300 pages, begins with the invasion of Iraq in 2003 and concludes with the withdrawal of troops in 2011. However, the authors have compiled a brief chapter describing the rise of the Islamic State (IS) and its eventual defeat by a U.S.-led international coalition.

Some key conclusions focus on political support, coalition warfare, and the relationship between conventional units and special operations forces (SOF).

The authors conclude that the political leadership failed by not providing a sufficient number of troops to the military commanders. They wrote, “The de facto cap on U.S. troop strength in Iraq and the reduction of ground troops in the Army’s transformed brigade combat teams (BCTs) combined to create an absolute shortage of ground forces for the prosecution of stability and COIN (counterinsurgency) operations in Iraq.”

It was only after General David Petraeus convinced politicians of the merits of his surge strategy that troop levels increased and violence decreased. The authors also argue that, in the event of a future conflict, the U.S. should not rely on its technological or qualitative war-fighting capabilities as a substitute for adequate troop numbers. Essentially, they are saying that there’s no shortcut to victory in a counterinsurgency environment.

The study also discredits coalition warfare. The authors argued that international partners were unwilling or incapable of achieving mission-critical goals, giving the example of the British forces, who had responsibility for southern Iraq and focused on the city of Basra. They argued that there was a significant lack of communication between the U.S. commanders in central Iraq and their British counterparts. As a result, there was a lack of strategic coordination. Further, when the U.S. commanders initiated the surge in 2007, their British colleagues were withdrawing troops and relocating them to Afghanistan.

With regard to special operation forces (SOF), the study singles out the Army’s Special Forces Groups, which specialize in, among other tasks, unconventional warfare (UW) and foreign internal defense (FID)—that is, training foreign forces. The authors argue that “during the wars in Iraq and Afghanistan, Army Special Forces groups increasingly focused on direct action, leaving large-scale FID missions to conventional forces—as is the case, at the time of this writing, in much of Operation INHERENT RESOLVE.”

On this day in history: The US invades Iraq

Read Next: On this day in history: The US invades Iraq

They also assert that there was a lack of cultural and situational understanding of the operating environment by most U.S. units.

For their research, the authors spent four years examining more than 30,000 pages of declassified documents and hundreds of hours of interviews. They also conducted original interviews with President George W. Bush and Secretaries of Defense Leon Panetta and Robert Gates, among other political and military officials.

You can read the full history here.