The foundation of Normandy over the course of the tenth century coincides with a period of dramatic change in the Frankish kingdoms, and it is only within the context of these changes that early Norman history can be understood. After most of Europe had been more or less united under Charlemagne and his sole surviving son, Louis the Pious, the return of multiple heirs led to a series of divisions of the regnum Francorum as Louis’ sons and, eventually, their sons as well came to various understandings as to who should rule what, and as at times some of them conspired against others to expand their holdings at their brothers’ and cousins’ expense. At the same time, external threats to the Frankish realm were increasing; throughout the ninth century, ever greater numbers of Scandinavian raiders were attacking the Continent and England, and eventually they even began to turn from raids to attempts at conquest. As early as the reign of Louis the Pious, Frankish kings tried to combat the Northmannic threat not only through purely military means, but by settling ‘friendly’ (or at least potentially friendly) groups of Northmen on Frankish soil, in hope that their new Northmannic allies would help protect them from other Scandinavian bands.
In 888, these two trends came together; at the height of an especially violent series of Northmannic attacks, including a lengthy siege of Paris itself, the East Frankish King Charles the Fat (emperor 881-887) died. Although the generations after Louis the Pious had been highly fertile, the death of King Charles left only one legitimate Carolingian in the West Frankish realm, later known as Charles Simplex or Charles the Simple, who was only a boy at the time. At a moment of extreme military danger, the western nobles did not want to trust their fate to a child, so they turned instead to a non-Carolingian, Odo (king 888-898), who had been the hero of the siege of Paris two years earlier and was thus a proven leader. The new King Odo was the son of Robert the Strong, who had been controlled Maine, Anjou, and the Breton March for Charles the Bald (king 840-877, emperor 875-877) before his death in 866, and had become the de facto ruler of Neustria (the lands between the Seine and the Loire). Odo and his brother Robert were still children when their father died, but gradually Odo managed to regain the honours his father had held, especially in the aftermath of the siege of Paris, and by the time he became king he was already the most powerful man in the western kingdom. Although Odo was seen only as a stop-gap candidate, and was succeeded on his death by the Carolingian Charles Simplex, he still set a precedent. From his day forward, the Robertines would have royal blood, and thus would have at least some claim to the throne.
Charles Simplex has had a fairly bad reputation (although recently historians have begun to appreciate him more), in part because of his unfortunate nick-name. Simplex means straight-forward, and means merely that Charles was not seen as Machiavellian, but it has often been mis-translated as the more derogatory ‘Simple.’ He was actually a rather effective ruler under very bad circumstances. But the previous century had seen a fragmentation of the West Frankish realm and central authority; where under Charlemagne local rulers (counts) were royally-appointed officials who often moved from county to county, and whose power was based on their position in the Carolingian hierarchy rather then upon a specific territorial power-base, during the course of the ninth century these officials began to settle down, establishing local dynasties of counts, and deriving more of their power from their county and less from the king. By the early tenth century, this process was well-developed, with local dynasties all across the future France. Several of these dynasties surrounded what would become Normandy, and were very important in its development.
Much of the territory that would become Robertine Neustria was first united in the hands of a family called the Widonids (Wido, or Guy, was a common name in the family) as the Breton March, in order to contain Brittany, which had never fully been integrated into the Frankish realm. In the middle of the ninth century, a Frankish ‘new man’ named Robert the Strong acquired Anjou, Maine, and much of western France north of the Loire. When he died fighting the Northmen at Angers in 866, his sons, Odo and Robert, were too young to succeed him directly, but gradually they managed to regain their father’s lands, and add more territory around Paris. Odo distinguished himself with his successful defence of Paris during its siege by the Northmen (885-886), and two years later he immensely boosted his family’s fortune by becoming King of the West Franks during the minority of Charles Simplex. By now, the Robertines controlled all of Neustria between the Seine and the Loire, and although upon Odo’s death the throne returned to the Carolingian Charles, his reign had set an important precedent; there were now two royal families in West Francia, although the Robertines were clearly the junior one. It is also of critical importance that Rollo and his successors settled in Neustria, and thus to the extent that the Rollonids participated in the Frankish political world, they were theoretically under the command of the Robertines.
Although the counts of Vermandois were newly established in the region north of the Seine in 911, they had an impressive pedigree. Direct male-line descendants of Charlemagne whose ancestors had been kings of Italy, in the second half of the ninth century they built a power base in the Paris region and then spread across the Carolingian heartlands around Soissons, Reims, and Laon. Because of their growing power and the prestige of their Carolingian blood, they were sought out for marriage alliances during the earlier tenth century by the Robertines, the Northmen of Rouen, and the comital houses of Blois and Flanders. Although the dynasty would suffer a rapid decline after the death of Herbert II (count c.900/907-943), at the time of Rollo’s agreement with Charles Simplex the house of Vermandois was one of the greatest powers in the Frankish realm, and played a key role both in the development of the Rollonid Principality and in the contest between Robertines and Carolingians.
To the north of Rouen, another principality was taking form during the ninth century in Flanders. The Flemish dynasty was founded by Baldwin I (count to 879), who seems to have come from a family of relatively unimportant counts, and who jumped into the major league in 863 by kidnapping and marrying Judith, the daughter of King Charles the Bald, against the royal will. By securing a papal blessing for his marriage, which seems to have been a relatively rare medieval love match, he forced King Charles to accept him; the king made Baldwin the count of Ghent, and later of the Ternois (near Boulogne) and Flanders. After Baldwin’s death, however, Northmannic incursions ravaged the Low Countries, and King Carloman decided to abandon the coastal region in order to concentrate his efforts on more-defensible areas. This presented a golden opportunity to Baldwin’s son, Baldwin II (count 879-918), who took the defense of the area upon himself, and in so doing seized effective control. Largely successful in his efforts against the Northmen, he attracted many Frankish soldiers looking for plunder and profit to his service, and also began an aggressive program of expansion southward into Boulogne and Artois (in Picardy). This expansion earned the enmity of King Ralph, who had his own plans for the area, but Baldwin was able to play Ralph and Charles Simplex against each other and maintain power over his expanded principality. Thus the fortunes of Flanders were set, and its counts quickly cast their eye open the county of Ponthieu, between Flanders and the Rollonid Principality, which would bring them into direct conflict with the Rollonids themselves.
To the west of Neustria lay Brittany, which had always been problematic. During the early Frankish period, Brittany had largely been left alone, but the Carolingians began to take an interest in it. The kings created the Breton March, which ultimately became the cornerstone of Robertine power, and launched frequent military actions designed to bring Brittany firmly into the Carolingian world. These expeditions were never entirely successful, and eventually the kings decided to acknowledge local Breton rulers who owed theoretical allegiance to the Carolingians. During the mid-ninth century, three effective and talented Breton kings expanded their territory eastward almost to Angers, and up into the Avranchin and the Cotentin in the future Normandy. But the nascent Breton kingdom was weakened by a succession dispute after the death of King Salomon, and by Northmannic incursions and even settlements. Still, in the at least theoretical claim of the Bretons to the Cotentin and the Avranchin lay the foundations for potential disputes with the Rollonids, as they expanded their own power westward.
Another area that would play at least an indirect role in the foundation of the Rollonid Principality was Lotharingia (modern Lorraine). Louis the Pious’ three sons divided the Frankish realm into three kingdoms. Two of these were the East and the West Kingdoms that evolved into Germany and France. But there was a third kingdom in the middle, extending from the Low Countries through Lorraine, Burgundy, and the future Switzerland into Italy. It was named Lotharingia after Lothar, its first king, and in theory it was the senior kingdom (it contained the ancient Frankish homeland, and its king was also the emperor). But almost immediately, the kings of the East and West plotted against the middle kingdom between them, and its existence was tenuous at best until the death of the last Lotharingian king in 869 without legitimate heirs. From then on, Lotharingia was subject either to division between the East and West Frankish kings, or to outright annexation by one or the other; it became a pawn in the game of Carolingian royal politics. In 911, the year of the agreement between Charles Simplex and Rollo, two important developments unfolded. First, the last Carolingian king of the East Franks (Louis the Child) died, and was succeeded by a German Frank named Conrad. And second, Charles took advantage of the power vacuum created by Louis’ death to seize Lotharingia. From uneasy beginnings, Charles Simplex had made remarkable gains: He had reunited two of the Frankish kingdoms under his rule, and he had blunted Northmannic assaults on his realm by allying himself to the Northmen of Rouen, who by guarding the Seine could protect the Frankish heartlands from river-borne Northmannic raids.
Thus by 911, a number of players participated in the game of Carolingian power politics. Charles Simplex ruled as king, but his power was not absolute; the Robertines controlled much of Neustria, except for the portion that had been lost to the Northmen (including Rouen, the heart of the future Normandy). The Northmannic territories comprised a no-man’s land, a power vacuum, which the Bretons to the west, the counts of Flanders and Vermandois to the east and the Robertines to the south wished to fill. Meanwhile, the Northmannic raids continued, most notably a large expedition that sailed down the Seine and attacked Chartres in 911; although the Northmen were defeated here, the battle made a considerable impression on the Franks, who realised that the Northmen could easily use the Seine and its tributaries to range widely throughout the Frankish realm at will. This was the landscape from which Rollo and his descendants would carve their new principality.
 Rosamond McKitterick, The Frankish Kingdoms Under the Carolingians 751-987, London: Longman, 1983 and the earlier chapters of Jean Dunbabin, France in the Making, 843–1180, Oxford: Oxford University Press, 1985, 2nd ed., 2001 provide a useful summary of events.
 Auguste Eckel, Charles le Simple, Bibliothèque de l’École des hautes études 124, Paris: Émile Bouillon, 1899 remains the best political narrative.