The phrase "was responsible for" is commonly used to indicate who or what caused a particular event or action. However, there are several synonyms that can be used to convey the same meaning. "Played a role in," "had a hand in," "contributed to," "was instrumental in," and "had responsibility for" are some examples of synonyms for "was responsible for." These phrases can add variety and depth to writing by allowing for different ways to express cause and effect relationships. By using synonyms, writers can also avoid repetition and keep their prose fresh and engaging.