I would say the biggest effect is that modern media makes America much more sensitive to casualties, in contrast to the past where broadcast-style media like TV and newspapers were essentially hijacked for uncontested government propaganda. I'm sure if an expert thought about it for a while he/she would come up with more stuff around homemade explosives/IEDs, small arms, and the like, but I think media is the main one.
So your theory is that lack of political buy-in from the populace, exacerbated by our access to technology and thus free information?
If that is the case, again, I contest that the real issue was fighting an unwinnable war for no real reason. Having a true, blue enemy to fight is an important difference. A war with China would be a Nazi Germany situation, whereas Iraq / Afghanistan were clearly a Vietnam.
