Perhaps you should try some spelling variations:
"american colonial empire" » "american colonization empire", "american colonial empires"
"american colonies empire" » "american colonial empires", "american coloured empire", "american colonialism empire"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"american colonial empire\") OR (\"american colonies empire\"))".
• Removing quotes may allow a broader search: (( american colonial empire ) OR ( american colonies empire )).
• Adding a wildcard symbol may retrieve word variants: (("american colonial empire") OR ("american colonies empire"))*.