In the mirror universe, Wilson was a North American dictator during the early 20th century. Sometime during his rule, Wilson was poisoned by his wife, who then continued to rule in his stead for five years. (ENT - Mirror Universe novel: Age of the Empress)

Wilson is presumably the mirror universe counterpart of U.S. President Woodrow Wilson, who suffered a stroke while in office, and whose infirmity was kept hidden by his wife Edith, among others.
Given that Wilson is described as "a North American dictator," it may be inferred that there was no single, unified Terran Empire at this point in history.
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