To describe a situation where multiple people or groups come together to act as a cohesive entity, you can use several synonyms for "ganged-up." One option is "teamed-up," which implies a collaboration or alliance among individuals. Another synonym is "united," which suggests a sense of solidarity or common purpose. "Conspired" is a more negative synonym, implying a secret or illicit alliance to achieve a common goal. "Colluded" and "plotted" are similar in tone, suggesting a deliberate and potentially devious coordination among multiple parties. Alternatively, "cooperated" or "collaborated" can be used to describe a more positive, mutually beneficial working relationship.