The need for mounted warriors (knights) to defend outlying regions from such raid required Kings to grant land and authority to nobles in return for loyalty and military service. The upper nobility would in hand over parts of their grants and authority to lesser nobles for the same loyalty and service. Thus defense of the realm and political authority became local and decentralized. This political system was known as feudalism. Feudalism could both be a stabilizing element for the defense and the growth of kingdoms and a destabilizing element fostering fragmentation and regionalism. Below is an account of the establishment of a powerful duchy within the kingdom of France made up converted and Gallicized Vikings known as Normans. Their leaders would not only control Normandy, but would also carve out kingdoms in England, Southern Italy, and the Near East.
THE BAPTISM OF ROLLO AND THE ESTABLISHMENT OF THE NORMANS IN FRANCE 
The king had at first wished to give to Rollo the province of Flanders, but the Norman rejected it as being too marshy. Rollo refused to kiss the foot of Charles when he received from him the duchy of Normandy. "He who receives such a gift," said the bishops to him, "ought to kiss the foot of the king." "Never," replied he, "will I bend the knee to any one, or kiss anybody's foot." Nevertheless, impelled by the entreaties of the Franks, he ordered one of his warriors to perform the act in his stead. This man seized the foot of the king and lifted it to his lips, kissing it without bending and so causing the king to tumble over backwards. At that there was a loud burst of laughter and a great commotion in the crowd of onlookers. King Charles, Robert, Duke of the Franks, the counts and magnates, and the bishops and abbots, bound themselves by the oath of the Catholic faith to Rollo, swearing by their lives and their bodies and by the honor of all the kingdom, that he might hold the land and transmit it to his heirs from generation to generation throughout all time to come. When these things had been satisfactorily performed, the king returned in good spirits into his dominion, and Rollo with Duke Robert set out for Rouen.
In the year of our Lord 912 Rollo was baptized in holy water in the name of the sacred Trinity by Franco, archbishop of Rouen. Duke Robert, who was his godfather, a Christian gave to him his name. Rollo devotedly honored God and the Holy Church with his gifts. . . . The pagans, seeing that their chieftain had become a Christian, abandoned their idols, received the name of Christ, and with one accord desired to be baptized. Meanwhile the Norman duke made ready for a splendid wedding and married the daughter of the king [Gisela] according to Christian rites.
Rollo gave assurance of security to all those who wished to dwell in his country. The land he divided among his followers, and, as it had been a long time unused, he improved it by the construction of new buildings. It was peopled by the Norman warriors and by immigrants from outside regions. The duke established for his subjects certain inviolable rights and laws, confirmed and published by the will of the leading men, and he compelled all his people to live peaceably together. He rebuilt the churches, which had been entirely ruined; he restored the temples, which had been destroyed by the ravages of the pagans; he repaired and added to the walls and fortifications of the cities; he subdued the Britons who rebelled against him; and with the provisions obtained from them he supplied all the country that had been granted to him.