He found the Government had no post-invasion strategy, no influence on the decisions of the US-appointed provisional authority in Baghdad and none of the British Government's objectives had been achieved by the time its forces were withdrawn in 2009.
The findings, of course, could be applied with even greater force to the US Government of the day. The Chilcot report gives all governments a manual on how not to go to war. But it is far more than that.
These sorts of inquiries are usually an exercise of wisdom in hindsight. Not this one. Just about all its findings match the foreboding of many people long before the invasion was launched in 2003. The operation was not a hasty decision.
The Bush Administration made its intentions clear the previous year. Not content with avenging 9/11 by driving al-Qaeda out of its bases in Afghanistan, Bush was intent upon a second Gulf War, with or without the backing of the UN.
Why? Some suspect it was to do what he believed his father should have done. The first President Bush had responded to Iraq's 1991 invasion of Kuwait with a US military operation that was well planned, had a clear, achievable goal, mobilised decisive force and, most important, kept to its plan and went no further.
The first Gulf War remains a model for the use of military power. General Colin Powell, chairman of the Joint Chiefs of Staff at that time, became Secretary of State for the second President Bush and amid preparations for "regime change" in Iraq, General Powell famously warned him, "You break it, you own it."
Since that invasion, the world has seen the volatile sectarian divisions within Islam that the dictators of Arab countries had managed to control. The Middle East and the West are more dangerous for the mistakes catalogued in the Chilcot report. Lessons must be learned.