When it comes to antonyms for the phrase "joins forces," the list can be quite long. Some of the words that represent the opposite of joining forces are resisting, opposing, dividing, separating, isolated, unconnected, withdrawn, disengaged, and uncooperative. These words convey the meaning of individuals or groups who are working against each other or have no relation or interaction with one another. It represents a lack of collaboration, communication, and teamwork. Therefore, the opposite of joining forces incurs a weaker, divided front, that lacks the strength and power that can only come from working together towards a common goal.