Roy, Arundhati. An Ordinary Person's Guide to Empire. Cambridge, South End Press, 2004
ISBN: 0896087271

Mohawk, John. Utopian legacies : a history of conquest and oppression in the Western world. John C. Mohawk. Santa Fe, Clear Light Publications, 1999
ISBN: 1574160400

Dukes, Paul. The superpowers : a short historyLondon, Routledge, 2000
ISBN: 0415230411

There are many, many books about imperialism in public libraries. My suggestion is to do a general keyword search for imperialism. The Roy title above, however, are general in nature and should be informative.