Koikaze...
I find the allegations in your post to be totally unsubstantiated and frankly off the deep end. Show me some evidence to support your views.
Yes, we have bases in Germany left over from the cold war, and I think most of us would love to bring our boys home from there now that the cold war is over but they are needed at the moment in support of our involvement in the Balkans (which I oppose). But is that evidence of imperialism?? Hardly, for if true, then we are doing a very poor job of it as shown by Germany's recent votes against us in the UN. Japan is not very good at doing what we desire either, nor is South Korea. They are not behaving as colonies, for sure.
I think your friend needs to study what colonialism/imperialism really is, and then see how many instances the US has been involved in it. There have been some over the years, to be sure, but all were short lived and probably no nation in the history of the earth has conquered more territory only to give it all back while spending literally billions of dollars to help the local people make a go of governing themselves in freedom.
Sometimes a grasp of history is necessary for perspective, and your friend needs a good dose of it in my opinion.
mlsoft