The phrase "were in the power of" refers to a state of being under the control or authority of someone or something. There are several synonyms that can be used in its place, depending on the context of the sentence. For instance, one can use "under the thumb of," "subject to," "at the mercy of," or "controlled by." Other alternatives include "dominated by," "enslaved to," "governed by," and "held captive by." These synonyms convey the same meaning and help to add variety and nuance to the language used, making the writing more interesting and engaging.