Software imperialism is control of code, e.g. wiki code, which is used to require data to conform to its expectations, e.g. a wikitext standard. This makes it all but impossible to create alternate software, and "locks in" a large number of users to a possibly inferior code base.
Microsoft Windows, Office and mediawiki are clear examples of this phenomena. The developers of both have strongly resisted any standardization that would allow any outside developers, much more competent as a rule, to compete with them to "manage" the vast text corpus stored using these user interfaces.