The way I understood Imperialism while I was in college was this. It is either for Political or Economic gain something is done. More often times then not the group of people doing it also feel they are better then everybody else. That they feel they are doing a service to the people that are on the land they are taking over.
This is where exceptionalism comes in. Lets go to the British empire and India. The British Empire felt that India was so backwards that it needed to be cultured. They tried to make them into little Englishmen and Englishwomen.
To continue on with that example. Gandhi tried to enter a Christian Church one Sunday and promptly he was thrown out because he was not white. So in the end the British people thought that they were superior to even those who they were trying to culture.
To bring it back to America Imperialism is dead because I don't know many people who even want to leave America. Most of us are quite happy to live and die here. The closest we had to Imperialism in the last 70 years was really two times. The taking over of Japan's government after WWII. McCarther wanted to make Japan a state, and the Korean war. which I am sure if McCarther won that he would have push for Korea being a state too.
We in America however are very much Exceptionalists. but then again so is everybody about their own country or culture. In America we say we are the most culturally accepting of all. However, when it comes to those coming into America from south of the boarder most of us become very agitated.
Now this is only how I understand it so please forgive me it is not a text book definition.
