I see your point about the aftermath of Pearl Harbor and the analogy with Japan and Germany. Good point. There are differences between Pearl Harbor and 9/11, though, and my concern is: are those differences sufficient to tip the balance in favor of outright colonialism, as opposed to mere isolationism? Here is the summary of the differences:
1) During WWII, the US was not involved in a unilateral invasion of the invading power. Rather, the US became involved in an already ongoing war, which it had attempted, thus far, to stay out of. The Japanese invasion was a part of an ongoing war in Eurasia, which brought the US into the ball game. The US then joined the Allied forces to stem the tide of Eurasian fascist imperialism. On the other hand, 9/11 was a unilateral terrorist attack carried out by a terrorist organization of religious zealots or fanatics, not an invasion by a nation. Furthermore, The US military response to 9/11 has been unilateral and, far from an international coalition of allies, the US has been targeted with international criticism, which it has chosen to ignore.
2) The casualties suffered as a result of 9/11 have scarred the American psyche far more deeply than those of Pearl Harbor. Pearl Harbor was a naval base in Hawaii--the casualties were military casualties and the site of the attack was relatively far removed. 9/11 took place in the US heartland, so to speak--Manhattan island, NYC. The casualties were civilian and far outnumbered those of Pearl Harbor. Naturally, this would result in a much greater psychological impact on the population of the USA--enough of an impact to alter the popular mindset in favor of a policy of colonialist imperialism? That remains to be seen. (I take the risk of sounding unsympathetic here--I'm just trying to be objective and I apologize to readers who might feel offended by my words).
3) To make a strict analogy with the aftermath of Pearl Harbor, the US should have restricted their military reprisal to Afghanistan--the only nation with a direct, proven connection with Al Quaeda. I completely supported the US invasion of Afghanistan and the toppling of the Taliban regime--partly because it was completely justified and partly because my own country of origin, India, benefited tremendously from the removal of the Afghan terrorist base, as India has suffered tremendously from Al Quaeda terrorism as well. What I OBJECT to, though, is an ongoing military campaign, with no end in sight, against the so-called "Axis of Evil"--a fictitious conspiracy of nations who have allegedly been linked with 9/11. This is an obvious fabrication on the part of the US administration to justify an ongoing international war that stands to be enormously profitable to certain concerned parties, most esp. the arms industry, the Bechtel group, the oil industry, and others who would benefit from such a policy of semi-colonialism. It's one thing to destroy the terrorist set-up directly responsible for 9/11 (which I totally support) and another thing to begin this ongoing policy of militarism against pretty much anyone one happens to disagree with. That strikes me as approaching colonialism and imperialism. Iraq is the first nation to have been attacked under this new policy of "aggressive isolationism", which looks, to me, a lot like colonialist imperialism. Who's next in line? Remains to be seen.
Finally, a point related to your points regarding the British and the Romans. Firstly, neither the British nor the Romans exterminated the population they conquered. Rather, they enslaved them by a process that they considered to be "civilizing the barbarians". They eradicated the culture of the enslaved nations and introduced their own culture and institutions into the conquered societies, remodelling them in their own image, so to speak. This definitely has its merits, but it is the essence of imperialism. They also harnessed the human resources of the conquered nations to feed their own imperialist machinery. That's one of the reasons they were able to keep the machinery going and keep it profitable. And another thing, both the Romans and the British were able to achieve a decisive military edge thanks, primarily, to technology. Their technology might not have been as advanced as ours, but it was technology that made their armies invincible. The Romans had their catapults, battering rams, etc., while the British had the Industrial Revolution--steam trains, sophisticated weaponry (for the time), etc. Moreover, the German Nazi war machine, which was, again, imperialist in nature because it was about the brutal conquest of sovereign nations, was even more explicitly centered around technology, most especially the Panzers or tanks, aircraft and the V2 missile technology (which didn't quite get off the ground, from what I understand). Thus imperialism and colonialism is definitely strongly connected with technology, which gives a nation a military edge. The Soviets, too, were primarily driven by their technological prowess, though they had a territorial advantage and superior numbers. However, the ultimate failure of the Soviet Empire was primarily linked to a failure in their technology, which was connected with economic failure. The Chernobyl disaster, which preceded the collapse of the Soviet system, is a clear example of the failure of Soviet technology.
As to whether Americans will realize that a colonialist policy will result in an increase of terrorism--maybe they figure that colonialist imperialism will increase their control over potential terrorist nations and, thereby, reduce the possibility of terrorism. Whether or not this is true, I don't know. But it does boil down to an ethical and diplomatic issue. My concern is--where do you draw the line. The US is certainly justified in invading and siezing control of a nation that poses an imminent threat to their security. My concern is: what constitutes such an imminent threat? The Bush administration argued that Iraq posed such an imminent threat owing to weapons of mass destruction. Critics argued that even if Iraq had weapons of mass destruction, it did not pose an imminent threat to US security. And, thus far, the Bush administration has yet to prove that Saddam Hussein's regime possessed any weapons of mass destruction at all. Again, if Bush can convincingly prove that his invasion of Iraq was justified because Iraq posed a significant imminent threat to US security and interests, I would support his action against Iraq. The mere toppling of a brutal dictator is not sufficient grounds to intervene in the affairs of a sovereign nation, because that amounts to a colonialist, as opposed to isolationist, agenda.
Again--if Iraq DID pose a significant imminent threat to US security and interests, and can be proven to have done so, the invasion of Iraq is justified. If NOT, then it amounts to colonialism, pure and simple. Maybe not explicitly so, but colonialism nonetheless. That's my point, in summation.