Complex sentence: As King of the Isles, Óláfr contracted marital alliances with neighbouring maritime rulers; he appears to have conducted successful military operations to reclaim the northern-most territories once controlled by his father, but may have witnessed the loss of lands in Galloway as well.
Split into simpler sentences: As King of the Isles, Óláfr contracted marital alliances with neighbouring maritime rulers. Although he appears to have overseen successful military operations to reclaim the northern-most territories once controlled by his father, he may have witnessed the loss of authority in Galloway as well.