You are joking right? Vikings never ruled Scotland, Wales or Ireland. They ruled Northern England for a short time before they were pushed out by the Saxons. The Vikings invaded Northern England years later ( and were defeated to a man at Stamford Bridge), at the same time that William the Conquer invaded from the south. It was the only way that they could defeat the Saxon Housecarls' shield wall. For the record, the Scots, or Picts, terrified the Vikings, and it is well known that the Vikings gave Scotland a wide berth.
Also, Saxon England was the most sophisticated country in Europe at the time, with its weaving, metal work, systems of common law, and taxes. This was the reason that William the Conquer and the Danes coveted the English throne so much.
Norwegian king Eirik Blod?ks ruled Northumbria for several years.
Danish king Svein Tjugeskjegg ruled entire England for 1 year, he was crowned king of England first christmas day in 1013.
Danish king Knut(Canute) den store ruled England from 1016 to 1035, with support from Norwegian Earl Eirik H?konsson who made the strategy and commands that made the conquering succsesful, he was made Earl of Northumbria.
Dublin was over many years dominated by both danish and norwegian rulers.
Norwegians established the first fortress there in 840, and Dublin was under danish and/or Norwegian rule untill 1014.
One of them, the Norwegian chieftain Torgils(Turgeis/Turgesius/Thorgeis) ruled from Dublin in 7 years, raided a lot of Ireland, and even worked to convert the irish people away from christianity and to the norse gods.
While northeast Scotland was highly influenced by Norwegians, since we also controlled the Orkneys, Shetlands, Faeroese, Iceland, Greenland, Hebrides and Isle of Man. Caithness in north-east scotland was under Norwegian control, by the earl of Orkneys, all up till 1266.
Yet, neither Ireland, Scotland or England was able to attack Norway not even one time, during the entire viking age.