"The enormous gap between what US leaders do in the world and what Americans think their leaders are doing is one of the great propaganda accomplishments of the dominant political mythology." -- Michael Parenti, Democracy for the Few.
There have been few military actions undertaken by the United States in modern history wherein the true intent is consistent with the rationalized motive. Consider the following historical anecdotes since the 1940s:
Japan, August 1945: Aside from the debate regarding the provocation of war with Japan, Americans use atomic weapons to kill at least 100,000 Japanese civilians [URC]. Truman justified his actions by citing figures regarding potential American military deaths resulting from a protracted conclusion to the war. Those figures were unsubstantiated (to the point of being fabricated); his action ignored other options recommended by his own advisers; the Japanese had made numerous attempts (known of by Truman) of reaching an agreement regarding surrender; and after the conclusion of the war, the U.S.'s own Strategic Bombing Survey reported that "in all probability" Japan would have surrendered before November 1, 1945 [Shalom]. While some still continue to uncritically accept the rationalization [Correll], it is clear Truman's priority was not the preservation of human life nor democratic principles, but vengeance and a desire to intimidate the Soviet Union.
"My staff was unanimous in believing that Japan was on the point of collapse and surrender." General Douglas MacArthur [Weber]
"This is the greatest thing in history." President Truman hearing of the destruction of Hiroshima. [Shalom]
Cambodia, 1955-1973. Nixon and Kissinger conduct secret "carpet bombings" of Cambodia (killing thousands) during 1969-70 to destabilize the government, resulting in its overthrow and the establishment of the Khmer Rouge by Pol Pot whom the US later supported though it was responsible for the deaths of hundreds of thousands.
"There are no American combat troops in Cambodia. There are no American combat advisers in Cambodia. There will be no American combat troops or advisers in Cambodia. We will aid Cambodia. Cambodia is the Nixon doctrine in its purest form...." President Richard M. Nixon, November 1971.
"In the event press inquiries are received following the execution of the Breakfast Plan as to whether or not US B-52s have struck in Cambodia, US spokesman will confirm that B-52s did strike on routine missions adjacent to the Cambodian border but state that he has no details and will look into the question." President Richard M. Nixon, November 1971. [Shawcross, via [Carvin]]
"I don't see why we need to stand by and watch a country go communist due to the irresponsibility of its own people." Henry Kissinger. [Cooper]
"I had the best seat in the house to watch that event, and our destroyers were just shooting at phantom targets — there were no PT boats there.... There was nothing there but black water and American fire power." James Stockdale, Navy pilot patrolling over the gulf at the time of the "incident."
"I don't know what more evidence we need." George Bush.
"... based on all credible information available to date ... the IAEA has found no indication of Iraq having achieved its program goal of producing nuclear weapons or of Iraq having retained a physical capability for the production of weapon-usable nuclear material or having clandestinely obtained such material." IAEA. [Bernays]
This is only a sampling of the most prominent deceits which I've had the time to investigate. In each case, independent of the actual campaigns, the U.S. government claimed its actions were responses to acts of despots and violence. Many of these claims were purposeful lies. In some cases, they were mistakes that were exploited for aggression but never corrected. In those instances where there was some legitimacy to a claim, truth was abused so as to justify America's complicity in the very same evils.
In no way am I excusing the crimes of any nation. Japan, Germany, Russia and many others have committed horrible crimes, but few have managed to do it under such a self-deluded banner of self-serving hypocrisy. One simply can not trust what government officials say and they must be held to a level of scrutiny that — unfortunately — does not exist. Instead, these incidents show half a century of deceit and media failure because of a reliance upon government sources for information, little verification of stories before reporting them as predicates for aggressive action, and an acceptance of rationalizations that are merely excuses for a course of action that has already been planned.