Restless energy, and a religion that taught its followers that death in combat alone conferred on the happy warrior a title to immortal glory and a perpetual right to the unbroken joy of battle daily renewed in Valhalla drove the Viking to war. Headed off on the south by the vast army and feudal system of Charlemagne, this energy in war could be exercised, and its religious aims achieved, solely on the sea, which skill in shipbuilding and in navigation as well had converted from a barrier into a highway to the west. As already stated, over-population in the sterile lands of Norway, and famine probably increased by immigration from the east and south, drove its people "at times in piracy and at times in commerce"[1] forth from the western fjords and The Vik across the North Sea to the opposite coasts of Scotland, and so to its western lochs and to Ireland, where they found cattle to slaughter on the nesses, stores of grain, and other booty. War, in fact, paid; and, after generations of harrying, many of the raiders concluded that the western lands in Britain were fairer and more fertile than their native shores, and desired to settle in the west. Finally the feudalism of Charlemagne was imitated by Harald Harfagr in Norway; and, against that, Norse independence revolted and rebelled. The true Viking would be no other man's man, and to secure Harald's feudal power he was driven forth from Norway by an organised navy manned by those of his countrymen who had agreed to accept King Harald as feudal overlord and to pay him tribute. Defeated, as we have seen, at the naval battle of Hafrsfjord in 872, the rebel remnant of the Vikings found their return to Norway barred; and those of them who became pirates in Orkney and Shetland and raided Norway as such, were, in their turn, assailed in these islands by King Harald, and destroyed. Others of them colonised Ireland, the Hebrides, and the Faroes; and from all these islands as well as from Scotland and Norway issued the swarms that settled in Iceland, and afterwards gave us a code of law, our system of trial by jury, much of our legal procedure, and, when crossed with Gaelic blood, produced the glorious literature of the Sagas. But in their exodus, whencesoever they started, what all alike sought was liberty; which, for them, meant the right to do exactly as they pleased to others, and freedom from paying "scat" or dues to a superior lord.