After the fall of Baghdad
...After Saddam's fall several elements were already in place for a disorganized resistance in Iraq. Saddam had already imported thousands of foreign fighters/thugs to control the country organized by his son as the Saddam Fedayeen. He had used this group as a harrassing force along the invasion route and many were destroyed as they "puddled" around Baath Party headquarters or Iraqi intelligence offices along the way. But, Saddam thought the main effort was going to be coming from Jordon and had placed many of these foreign fighters in Anbar province which was not on the invasion route after the Turkey front was lost.
My own guess is that the subsequent violence was the result of two things. As soon as Saddam fell, forces opposed to the US began to plan and execute their riposte with remarkable speed. Ex-regime elements, Islamists etc. began to make their move. In contrast, the Coalition was unable to both take control of the post-Saddam situation and respond to enemy countermoves. There followed a period in which the Coalition was forced on the defensive all across Iraq. And that continued until the Coalition was eventually able to learn, adapt and regain some initiative.
The stories related by the Educated Soldier illustrate the lack of continuity in the script. Having defeated the Iraqi Army, the idea was that it was "over". In retrospect things had only just begun. But not only was the force mentally unprepared for what came next, it was physically and organizationally unready. There were inadequate numbers of interpreters; I suspect that intelligence networks were underdeveloped; probably most importantly, the force was unfamiliar with Iraq. When the trouble began, much of the attention focused on the "armor" gap. The striking difference between 2003 and 2007 is not the lack of steel plate on the Humvees -- something which obsessed the media for a long time -- but the difference in attitude and doctrine between that era and Gen Petraeus' force.
The fateful decision of Paul Bremer to dismantle Saddam's Army may have saved Iraq from a continuation of the fallen regime under other color; it might have avoided a Shi'ite insurgency that may have developed in response; it might had many things to commend it in the long run. But off-handedly dismantling the ancien regime without the Coalition capability to take up the slack meant that for some years it would be operating in a debatable void....
Another element of the resistance was made up of the Sunni tribal groups who had help Saddam control the Shia and Kurds after the first Gulf War. These are the groups that are now rallying to our cause in fighting al Qaeda and they probably make up the biggest lost opportunity after the fall of Baghdad four years ago, but he political cost of reconciliation with them at that point would have been difficult because of their association with prior suppression efforts.
The Former Regime Elements were the third group who at some point led some organization to the resistance. These are the people who maintained control of the Iraqi people through brutal repression when Saddam was in power and they continued to do their thing after he fell, the main difference being that now there were people who could fight back against them.
There are many who argue that the disbanding of the Iraqi army was a mistake. The fact is that at the time Bremer made the decision there was not much of an army to disband after it did an en mass fair well to arms during the course of the invasion. Reconstituting it would have been almost as difficult as starting over like we did.
Finally wars take a course that neither side entirely controls as long as both want to continue to fight. Each side reacts with the forces they have to defeat the strategy of the other. As one element works forces are brought to bear against it to make it not work. You see the evolution of the fight over the course of the war and sometimes do not see the big picture. Very few people in this country realize that 90 percent of enemy IEDs are found and destroyed before they can be used against us. This requires the enemy to use ever greater resources to ever smaller results, but the only result he is primarily aiming for is the headline of one effective blast and his has a compliant media to give him that.