This is a good question, but one that is extremely broad. As you know there were many wars that America was part of and for this reason there were many different kinds of impacts.
For example, in World War II, there was a feeling of victory and pride. The reason for this was because everyone knew that we were fighting an evil regime that needed to be stopped. In light of this, American morale was high. And because the war was fought away from home, America fared well in many ways economically.
In Vietnam, there was much more of a mixed reception. Some really hated the fact that we were in war and many became disillusioned with the American government. This feeling still lingers in some ways.
When we come closer to our times, many feel upset that we went into Iraq based on faulty information. As you can see, the impact is mixed to say the least.