Breaking News: Guerilla Tactics Work
Wikipedia has a nice article on the Irish War for Independence. It is a war well worth studying, as it was the first modern war against colonialism and relied heavily on urban terrorism.
Another war worth examining was the Algerian war for independence (not only is the film Battle of Algiers a masterpiece, it is also an expose of why defeat is inevitable if one side is seen as occupiers.
Given that the historical antecedents were there... the question then is: why did the advocates for the invasion believe that victory was self-assured? Especially when many of them knew that the case for invasion was based on lies?
The evidence available suggests that the answer is hubris. Given the nature of things, this is turning into a Greek tragedy--the kind where there are no victors, there are no lessons learned, there are only a whole lot of dead people and tears.