(1):

(n.) The policy, practice, or advocacy of seeking, or acquiescing in, the extension of the control, dominion, or empire of a nation, as by the acquirement of new, esp. distant, territory or dependencies, or by the closer union of parts more or less independent of each other for operations of war, copyright, internal commerce, etc.

(2):

(n.) The power or character of an emperor; imperial authority; the spirit of empire.