Why do people talk about the decline of American power? Where is the evidence?

[Sevengen]

@ the OP,
..... you stated;
"One other thing to get clear about the Iraqi war is that the actual war, that is, defeating Saddam Hussein's troops, and ending his regime was won in about 6 weeks. Far quicker than the previous encounter with Iraqi forces during the Gulf War, which lasted about 7 and a half months."

not trying to argue with your post, as it's an interesting topic, but I'd like to point out something in reference to your above comment.
Operation Desert Storm; which is when the American and Coalition forces commited themselves to an aggressive, 'offensive' action began in mid January of 1991- as opposed to Operation Desert Shield which was an initial build up of forces and 'defensive' military posture for Saudi Arabia that began in August of 1990.

Operation Desert Storm, an offensive military action designed to remove Sadam's troops from Kuwait, began on January 17, 1991. This is when the actual 'war' between Iraq and Coalition forces started. By February 26th, Iraq forces were retreating from Kuwait and two days later, 100 hours after the actual ground war had begun, President Bush called a cease fire and declared Kuwait liberated.

The goal of Operation Desert Shield was to remove Sadam from Kuwait, this was achieved in roughly 5 weeks, not 7 and a half months.
The military goal of the second Gulf War was to remove Sadam from power, this was also achieved in roughly the same time frame.