There are several synonyms for the phrase "showed cause." One such synonym is "demonstrated reason," which means to present evidence or argument to prove a point. Another synonym could be "provided justification," meaning to give a valid explanation or reason for something. Furthermore, "established grounds" could also be a synonym, indicating that a convincing and credible foundation has been laid for a certain claim or action. Additionally, one could use "proved motivation," suggesting that a clear reason or purpose has been established. Ultimately, all of these words and phrases imply that there is a strong basis for a particular argument or course of action.