When Vikings swept the western Europe, all European countries were faced with great disasters. Meanwhile, the Britain Island on the Atlantic Ocean, became the main plundering target for Vikings. At that time, England, Scotland and Wales were not under the same flag, and even all of them were internally divided. This was a great opportunity for Vikings.
At that time, Scotland was in a four-party civil war. Strathclyde (Britons, a subdivision of Celts) and Northumbria (Anglo-Saxons) were in the southern Scotland close to England; the highlands in the northeast was occupied by Picts; Dalriada in the western coastal area was ruled by Gaels.
Norse could went straight to the Isle of Man and even Ireland via Shetland Islands, Orkney Islands and the Hebrides. Besides, Sutherland and Caithness in the northmost part of Scotland were also on this route.
There would be no peace as long as those barbarians were here. Picts and Dalriada were the first victims. The Pict-Dalriada allied army was disastrously defeated by Vikings in 839, and both of their kings were killed in battle. At first, the other two kingdoms in the south “only” suffered frequent plunders. But Vikings in Dublin (in 853) and York (referred to as Jórvík at that time; in 867) soon extended their hands here. In 870, the capital of Strathclyde Dumbarton was under siege. The city fell four months later, and the king was sent to Dublin and executed; Northumbria had only half of their territory left after losing York, and they lost the other half in the Viking invasion in 874. The Viking invasion reshuffled the existing order, and all four kingdoms were greatly weakened. The situation in Dalriada seemed to be better: this kingdom of Gaels took this opportunity to gradually annexed their weaker neighbors, and finally founded the Kingdom of Scotland. As for those islands, the centuries-long rule of the Norse just began.
Wales was not a favored destination for Vikings. Llanfaes, the capital of Gwynedd (one of many small Welsh kingdoms) on Anglesey Island was plundered by Danes in 853, but it remained to be the capital of Gwynedd till the 13th century. It seemed that people there did not find the threat from sea serious.
The traces that Vikings left in Wales were mainly on the northern and southern coasts. These traces were more like some Viking “pilfering” when they passed by. But the local kings in Wales tried to take advantage of Vikings. In 878, with the help of Danes, Wales defeated their nemesis Mercia; and during the Battle of Buttington in 893, Welsh joined Wessex and Mercia in attacking Vikings. That was totally pragmatism. But in the 10th century, with the redirection of Anglo-Saxons’ offensive and the strengthening of defense in Normandy, Wales became a soft target for the increasingly more pirates coming here. Anglesey Island was plundered again in 987, over two thousand people were kidnapped for ransoms from the king of Gwynedd. But that was the end of the suffering of Wales. Compared to Scotland which lost a large number of noblemen, Wales was much luckier, as they never experienced large-scale Viking colonization or invasions.
It was Welsh who led Norse to England. In fact, Wales did not border Wessex. They were separated from each other by the Bristol Channel. Severn River, the longest river in Britain (actually 350 kilometers long), falls into this bay. The Severn River originates from the northeastern root of Cambrian Mountains which was originally Welsh territory. But as early as the Roman times, Welsh people had been forced to moved back into the Cambrian Mountains and struggled to live in those coastal lowlands. Geographically, the Kingdom of Mercia occupied the Severn River basin during the Heptarchy. With the Cambrian Mountains, Welsh people were still able to fight against one single English kingdom. But the problem was, Welsh were already in peril when the West Saxons conquered Cornwall and began to end the Heptarchy (in fact, the war on Wales had already begun).
In order to avoid the same fate as Cornwall, Welsh made Norse believe that they could gain larger profit from England through cooperation. This time, Welsh were active to assist Vikings with an obvious strategic purpose: let Vikings destroy the unification progress of England. After entering the Bristol Channel, Vikings rendezvoused with Welsh setting off from the north shore of the bay. They went upstream along the River Avon, a tributary of Severn River, all the way to the central England. Although Wessex was not their direct target, but as “the ruler of Britain”, West Saxons could not watch Welsh and Norse rampaging in England. At last, West Saxons repelled the Welsh-Norse allied army on the upstream of River Avon in 838 AD and ended this crisis. But this was not the largest challenge for England. Danes would landed on the eastern coast of England soon.
The terrain of England, which is high in west but low in east, decides that most of its rivers flow from the west to the east and finally into the North Sea. Thames River is the most important river, and the one of the best geographical conditions in England. During the Heptarchy, the Thames River to the west of London was the border between Wessex and Mercia as well as Essex (London belonged to Essex). In the 850s, Danes began to appear in the Thames Estuary. Using the Isle of Sheppey as their springboard, these pirates in dragon boats frequently harassed the lower Thames region, including London, which was repeatedly plundered. It meant that the Kingdom of Wessex would be under the direct threat of Danes if they just let the situation run its course and did nothing.
Compared to Norse, Danes were more ferocious and aggressive. But West Saxons, who were still on the rise, successfully repelled Danes and dashed their dream of expanding towards the south of Thames River. But they had a problem: England has a long coastline, and the Danes could always find some vulnerable spots. As the strongest kingdom in England, West Saxons must took up the responsibility of protecting the whole England from foreign invasions. But facing the threats from the sea, they also had a long coastline to defend. Under such circumstances, if Danes chose somewhere far from Wessex to break in, it would be difficult for West Saxons to help other kingdoms to defend against invaders.
And for Vikings, the bays that connected long or many rivers were the most ideal landing locations. They could not only establish strongholds by the bays, but also go deep inland along the rivers, and thus expanded their scope of plundering. The funnel-shaped Thames Estuary was not the only ideal place for landing. There were at least two similar-shaped bays or estuaries in central England that met Vikings’ requirements: the Wash and the Humber Estuary. As a matter of fact, that was the same route where the Anglo-Saxons landed in England in the past. The Thames Estuary and the southern English coastline were where Saxons and Jutes landed (Saxons founded the Kingdoms of Essex, Wessex and Sussex, while Jutes founded the Kingdom of Kent); and the Wash and the Humber Estuary were where the Anglos disembarked. The largest ones among seven kingdoms, Northumbria, Mercia and East Anglia, were founded by Anglos.
In 860s and 870s, Danes launched several large-scale offensives in northeastern England. A vast territory of Essex, East Anglia, Mercia and Northumbria fell and was occupied by Danes. What was more scary was, the Danes planned to give up their precarious occupation, piracy; and use England, which was of better climate and agricultural conditions than Denmark, as a colony. The same change also occurred on Anglo-Saxons; they were brought to Britain by Romans as mercenaries, but in the end their expedition turned into a migration.
During the war against Danes, England also produced the only monarch with the postfix “the Great” – Alfred the Great.