This article seeks to approach a highly discussed, central Philosophical-Political issue: the problem of the basis or the justification of the State. The State -or political unity- does not carry out tasks supported only in persuasion and affection; the force is also an esential means for its action. The question about the justification of the State allows two answers: the one that denies the possibility of justification (anarchism and marxism) and the one that accepts the possibility of justification. Among the last one it's possible to distinguish a "negative" justification, that shows how can the State overcome the situation of prestate disorder, and a "positive" justification, that emphasizes the goodness of community lije that is reached in the polis or political unity. The article shows the insufficiency exposed by the anarchist and marxist denial of the State. Later the two modes of justification are basically approached, within highty relevant authors for the history ofpolitical philosophy: Aristotle, Augustine of Hippo, Thomas Aquinas, and Kant. In short, the article attempts to show that, well understood, the "positive" basis of the political unity allows the overcoming of those problems that the "negative" (basis) leaves unresolved.