Neustria was the Merovingian term for Normandy, or an ancient Frankish kingdom's word for the region of Northern France across from the English Channel. From ancient times, this region has specifically denoted the northern part of France, around Cherbourg, for example, as compared to Burgundy, which was part of Austrasia. Viking invasions ensued and resulted in the settlement of many Scandinavians in both England as well as the mainland European coast, inclduing France, Germany, and even as far as Russia. After the settlement of England and France, the Viking ruler Rollo used his northern French conquest to establish a fiefdom and position as Duke of Normandy (Brittanica). His ancestor, William the Bastard, would eventually conquer England and become King in 1066 as William the Conqueror. Smith seeks to draw the parallel between Rollo the Duke of Normandy and his invasive, brutalistic descendants along with that of the current French ruler, Napoleon.

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https://www.britannica.com/place/Neustria