Antonyms for the word "reunify" include words such as "divide," "separate," "split," "dissolve," and "fragment." These words signify a disconnect or separation rather than bringing things together. While reuniting means to bring together or unite, dividing means to break apart or separate. Similarly, splitting and fragmenting are the types of action that lead to separation, which is the opposite of reuniting. Dissolving also signifies a separation or breakdown of something that was previously united. Thus, the antonyms for "reunify" essentially describe the opposite of the unification or the bringing together of people, things, or countries.