The Duchy of Bar originated as a small border state under the authority of Upper Lorraine, part of the Holy Roman Empire. The fortress of Bar-le-Duc protected the realm of Lorraine from the Counts of Champagne, who swore allegiance to the Kings of France. When Duke Frederick III of Upper Lorraine died in 1033, the region of Bar first appeared as a distinct county when his sister inherited the title.

Though the area west of the river Meuse/Maas had been de jure French since 843, in 1297, King Philip IV asserted direct authority over the region. The Kings of France now granted the counts of Bar a ducal title. This meant that France and the Empire claimed the territory as their own. Eventually, the Holy Roman Empire recognized the French claims east of the Meuse/Maas. This recognition by both sides gave the Dukes of Bar representation in the Parliament of Paris and the Imperial Reichstag.

By 1500, the Dukes of Lorraine had inherited the Barrois crown, and the two regions would never be separated afterward. Though always a Francophone region bound to the court in Paris, the territory would not become part of France officially until 1766, when Lorraine was annexed.

As a border region, castles and fortresses cover the North of Barrois. These fortifications strengthened as French influence grew, especially following the 18th century. However, the 19th and 20th centuries visibly scarred the region with lines of trenches and cataclysmic battles. Several lines of late 19th century fortifications once divided the French and German Empires. But the scars of the First World War dominate the landscape, especially around Verdun. The war came at a significant cost to the region, and its historical heritage is found only in a few scattered towns, monasteries, and fortresses.