First, as I've said, the decision was purely formal since the army self-disbanded. I had hoped our efforts to get Iraqi units to defect intact would work to provide a core for a new security force. Strategypage notes that Iraq is now asking officers up to the rank of major to return to duty. This is the rank I figured we should keep as a rule except where there is demonstrable question of loyalty. Ranks above major should be excluded except for proven loyalty to the new Iraq. But the army went home so this wasn't possible anyway.
Second, some advocates of keeping the army intact even if we could, note (as Strategypage states) that we kept German and Japanese forces intact until we could gain control so why shouldn't we have done the same with Iraqis? My response is that the Germans and Japanese formally surrendered and so their officers obeyed their leaders' orders to cooperate. By contrast there was not only no formal Baathist surrender but a Baathist plan to launch an insurgency after the major combat operations were lost. So employing existing units (if we could have recalled them from their capitulation and flight to their homes) would have put people in our pay and who would have probably worked for the insurgency.
Third, once it was clear that the Shias were grateful but suspicioius of us, anything short of thorough de-Baathification would sow too many doubts and hinder the goal of getting Shias to back us enthusiastically. The Shias are with us so it is safer to bring in former regime officers. The "major" threshold is probably still wise.
Strategypage summarizes the dilemma:
Nearly all the key officers in the Iraqi armed forces were Sunni Arabs, and selected mainly for their loyalty to Saddam Hussein and the Baath Party. Thus Bremer and his staff had to make a quick decision. Do they allow several hundred thousand organized troops, led by minority, and much hated, Sunni Arabs, remain in their jobs, and risk having these troops becoming the basis for warlord forces, led by men who had long supported dictatorship? Or do you disband the army, and start over? Either way, there are risks. What would you have done?
At least they acknowledge a debatable point. Disbanding the army was not a clear mistake.
What would I have done? I would have disbanded the Iraqi army and started over, with the "major" rule in force. In hindsight, I would have focused on light infantry instead of a conventional army as we did in the first year when we assumed no major insurgency. I couldn't know that, however, so I probably would have focused on a conventional force just as we did.
So don't call disbanding the Iraqi army a mistake. We are winning after this so-called "bad" decision, and advocates of the mistake argument can't demonstrate that the bad things that could have happened from their preferred course wouldn't have happened.