There was a fundamental difference in the soliders we sent ot Vietnam too, average age was much younger than WWII & Korean War, these guys really didn't know what they were fighting for, they weren't old enough to value the rights & liberties valued by our country. Shey were also socioeconomically disenfranchised, anyone with money or a family with political clout got out of active duty, look @ our last 2 presidential candidates, one war photographer/journalist , one in the National Guard.
The all volunteer military is a little different animal. They want to be there for one reason or another.
There were many factors involved in why we withdrew, largely, the American public just didn't have the stomache for it, and they were probably right.
What we'll be doing in the Middle East @ first a show for the American public, then the real work will begin, rebuilding the CIA, NSA, & FBI's human part of the spy business. What good are all those cool satellites etc, without our very own James Bond? I think we need to make Tom Clancy an offer he can't refuse to be a spymaster...