During the 14thcentury, the principality of Bar progressively turns into a genuine State. The prince relies largely on its seigniorial legacy. The dynasty is unchallenged. The domain, rather large for the region, is efficiently ruled and defended, in spite of insuficient ressources. In building the State, the prince can rely on an important network of obedient liegemen, an emergent elite of commoners, mainly financers and scholars, but slightly less on a weak Church which, incidentaly, does not have a proper financial support. Since 1301, the prince is a liegeman of the king of France for the "Barrois Mouvant". The king tries to introduce some elements of sovereignty but meets failure, except for judiciar appeals. He can nevertheless count on the prince of Bar who, in addition to being a faithful liegeman, is a true french lord, raised in the royal court and, after 1364, brother-in-law of the king. The shaping of the State has thus a french influence. The sovereignty of the prince of Bar can nearly express itself in its entirety, even in the "Barrois Mouvant". The central government grows thanks to the establishment of secretaries and of an Court of account. The Household, witness of the splendour of the prince, grows too. The State asserts itself in exercisinig justice for which the local administration is strenghened. To deal with the debt of the prince, a new tax system is introduced. This State has to face the neighbouring principalities for the hegemony over the region, but the forces being equal a statu quo is maintained: the matrimonial union between the principalities of Bar and Lorraine is an inevitable evolution.