On 9/11 +1 I began advising anyone who would listen (i.e., no one) that the US government had an opportunity to attack the sources of major dangers in the Middle East and I recommended (to empty air) that the first target ought to be Iran.
Governments of democracies surely, and probably nations having other kinds of governments as well, have, in most times, difficulty moving the nation to war. A good example of this is given in Churchill's "Gathering Storm." Churchill tells us that, in English politics, he ranted and raved, warning of the rise of Nazism in Germany, and insufficiently many people listened. Had Great Britain and France, or just France alone, acted when Hitler occupied the Rhineland in March 1936, in breach of the Versailles Treaty (forced) and Treaty of Locarno (freely-negotiated), Hitler's career might have been forced into a quite different path than it actually took. Perhaps Mein Kampf was not a sufficiently obvious warning to the French of Hitler's intentions and capabilities. Without France, Great Britain could do nothing.
By the time Hitler went after Czechoslovakia, it was obvious to some that this was likely to be the last time France and Great Britain, assisted as they were by the USSR and Czechoslovakia, would be able to have a clear military superiority over Germany. Yet, Neville Chamberlain, leading the others, caved in and bought, so he thought, "peace in our times."
Avoidance of war even when war seems the rational course, seems a pattern of democracies. I suspect that the pattern is modulated by biology. War is avoided, by the populace, when its proportion of warrior-aged men is low enough. War being more likely otherwise. But, we, in the West, have been in a long period of low birth rates, and getting the US to go to war takes something like a Pearl Harbor. And we see today that even that is not enough to sustain a war mood for long.
Had I been imperial consul of the US forces on 9/12, I would NOT have wasted time, and the limited duration of war mania, on Afghanistan or Iraq. I would have PRETENDED to go after Afghanistan. I would have, assuming of course that clearer and superior minds had not dissuaded me, issued an ultimatum to Iran to clear the way for US troops to move from the Persian Gulf into Afghanistan. And, by the way, open your nuclear facilities to inspection by US experts. Had Iran complied, and been found to not have a significant nuclear program, well and good, on to Kabul. But, more likely, Iran would have spat in the face of the US ambassador and I would have had my war. And I would have moved the US as swiftly as my kicking of ass could make it move (probably I would have had to fire Colin Powell). One of my eyes would have been on the clock. War moods do not last forever. Not in a population which is fat and happy, having insufficient fears to re-stir martial, patriotic emotions.
My attack would have been, initially, more costly than was the invasion of Iraq. But, the main danger would have been dealt with first. Afghanistan hardly counts and Iraq would have been more easily intimidated once its much stronger neighbor had been humbled.
Attacking Afghanistan was the weakest of the three options. Weak not only in required effort but in results. Iraq was second weakest. In my present understanding, it seems to me that the US moved in the wrong order, squandering the period of martial emotions on the easiest problem. And now, we cannot complete the job because the will of the people has, as predicted, waned.
Iran can shut down the flow of oil from the Persian Gulf, the jugular vein of the hated West. With nuclear armed missiles some crazy Iranians (do you think, possibly, some of them are?) might think they can do this with near impunity. I do not know what we can now do about this growing threat.