conflict, disaccord, discord, discordance, discordancy, disharmony, dissension(also dissention), dissent, dissidence, dissonance, disunion, disunity, division, friction, inharmony, schism, strife, variance, war, warfare

clash, collision, competition, contentionaltercation, argument, bicker, brawl, debate, disagreement, dispute, divide, fissurefalling-out, fight, hassle, jar, miff, mix-up, quarrel, row, run-in, scrap, spat, squabble, tiff, wrangleincompatibility, incongruence, incongruity, incongruousness, inconsistence, inconsistency, inconsonance, inharmoniousnessanimosity, antagonism, antipathy, cold war, enmity, hostility, ill will, rancor