The first thing to understand when thinking about this question is that not everyone in the United States reacts to and reflects on war in the same way. Different people will have different thoughts about war. That said, we can at least generalize about the changes in our reactions to war since the end of World War II.
I would argue that our reaction to war has changed since WWII in that we have become less certain about the moral correctness of our wars. World War II was a war that essentially everyone in the United States agreed on. People believed it was a war that we needed to fight and they supported it wholeheartedly. After WWII, though, Americans became less and less convinced of the rightness of their wars. This was especially true of the Vietnam War and, eventually, of the events that followed the invasion of Iraq in 2003. Because we are less morally certain about our wars, we have a harder time celebrating them and the people who fight them. We support the soldiers, but many Americans are less able to feel really good about the wars.
Another change is in our relationship to the war efforts. In WWII, Americans were all affected by the war. A large percentage of the male population of the right age was in the military. People were affected by rationing. Essentially all Americans shared in some way in the sacrifices necessary for waging war. Today, our wars are much more limited and there is much less sacrifice. Our soldiers and their families make serious sacrifices, but most Americans do not. This means that we feel less connection to wars today than we did in WWII.