I was reading through some of the early kings of Scandinavia and I stumbled upon Harald Wartooth. On his wiki page it says he subjugated both Denmark and Sweden and also all the territories in England that belonged to Halfdan the Valiant and later Ivar. However it also says that he died during the Battle of Bråvalla apparently about the year 770 or 772. This is clearly before the vikings started raiding England, so I'm a bit confused. Is the wiki wrong here and if so, in what way?
Well, first off, Haraldr hilditönn, Ívarr inn viðfaðmi, and Hálfdan snjalli were legendary kings, so any information you're reading about them is instantly suspect; the earliest sources we have for these 6th, 7th, and 8th century kings are 12th century legends.
Second, 793 was the first recorded raid of a monastery by víkingar, but there is no doubt that the Scandinavians were trading, raiding, and selling their services as mercenaries to the English well beforehand.