antagonism (n.)

"state of being mutually opposed; opposition between two things or against something," 1797, from French antagonisme or directly from late Greek antagonisma, noun of action from antagonizesthai "to struggle against, oppose, be a rival," from anti "against" (see anti-) + agonizesthai "to contend for a prize," from agon "a contest, a struggle" (see agony). Milton used antagony as a noun.