Duchy of Krnov was created in 1437.
A republic is a form of government which is not rules and aristocrat: a king (monarchy), prince (principate) or duke (duchy). a republic can have any king of political regime, so long as it is not rules by an aristocrat. It can be a democracy, an authoritarian state or a dictatorship. Most modern countries are republics.
Originally, dukes were men in the Roman army who had achieved the rank of general, but could not hold it because they were not Roman citizens by birth. Early in the Middle Ages, the title was pretty much interchangeable with the title of general. It quickly became a term for a man who controlled a large piece of territory and maintained a powerful fighting force. In this capacity, it was a title of nobility, higher than count or earl. By the time of the High Middle Ages, it was the highest title of nobility, though it was below that of any royal rank, such as prince. In some places, dukes were monarchs in their own right. As such they were often called archdukes. Monarchs whose ranks were of nobility rather than monarchy were prone to deciding they were kings, however.
Eleanor of Aquitaine was the daughter of William X, Duke of Aquitaine, and Aenor de Châtellerault. Her father was a powerful nobleman in France, and her mother was from a prominent family, which helped bolster Eleanor's status as one of the most influential women of her time. Eleanor inherited the vast duchy of Aquitaine upon her father's death, significantly enhancing her political power.
The Visconti dynasty ruled the duchy of Milan during the period 1277 to 1447. They were responsible for the constrruction of the Duomo, or Milan Cathedral. At various times their holdings included many other cities, notably Pavia, Verona, all of Lombardy, Como, Ticino and Pisa. The last Visconti had a daughter who married a Sforza, who then established the next ruling dynasty in Milan.
The Mountain was created in 1793.
Duchy of Krnov ended in 1623.
Krnov was created in 1221.
Duchy of Urbino was created in 1443.
Duchy of Carniola was created in 1364.
Duchy of Friuli was created in 569.
Duchy of Florence was created in 1532.
Duchy of Württemberg was created in 1495.
Duchy of Żagań was created in 1274.
Duchy of Brzeg was created in 1311.
Duchy of Belz was created in 1170.
Duchy of Teschen was created in 1281.
Duchy of Merania was created in 1153.