This paper tackles the issue of conflict within the framework of political realism. It aims to define what conflict is and to show that it is inevitable. I put forward a definition of conflict that pulls together two strands present in the literature: the presence of incompatible preferences and the disposition to impose them against the resistance of others. This second element is particularly important as it allows to neatly distinguish conflict from other similar concepts, like pluralism or disagreement among which it is sometimes confused, and to understand better its subcategories, violence and war. From these analysis, I extrapolate four significant features of conflict, which are appropriately highlighted by this definition: the relation to politics, the connection to violence, its neutrality to content and its unilateral emergence. Given its unilateral emergence, as long as even few people exhibit incompatible preferences and the disposition to impose them, conflicts would spontaneously emerge. This support the conclusion that conflicts, appropriately understood, are permanent features of the human world. Finally, I show how this analysis reflects on political philosophy. While the mainstream view of Rawlsian liberalism tends to underestimate the inevitability of conflict, the tradition of political realism captures it in a more satisfying way.