Prior to 800 CE the regions that later became Norway were fragmented. However, with farming communities constantly under threat of attack by bands of robbers and homecoming Vikings, petty kingdoms began to evolve. Some became quite powerful, eg the Trøndelag earls of Lade, whose power increased steadily during the 9th century. Eventually, after a battle at Hafrsfjord (near Stavanger) in c872, Harald Hårfagre (Harald Fairhair), king of Vestfold (on the coast, south west of modern Oslo) became ruler of a large area of the country. However, the unifying process, involving harsh struggles between warring Norwegian chieftains, was to continue until 1060.

This process was set into motion during the rule of Olav I Tryggvasson (968-1000), a descendant of Harald Hårfagre who sponsored missionary activity from England, Germany and Denmark, and was consolidated during the reign of Olav II Haraldsson, also called Olav den Hellige, ‘Olav the Sacred’, (1000-1030), who died a martyr’s death at the Battle of Stiklestad, giving him saint’s status. The first bishoprics subsequently appeared in Norway – Nidaros (later Trondheim) in 1029 and Bergen in 1070. An archbishop was installed at Trondheim in 1152.