Update: The suspect in custody is described as a right-wing Christian fundamentalist opposed to multiculturalism, etc. Thus, this apparently had nothing to do with Norway's involvement in Libya and Afghanistan.
Someone quoted in this piece about the attacks in Norway says they will "change everything." Hyperbole, but understandable in the immediate aftermath of shocking events.
Targeting young people attending a summer political conference is especially despicable. The linked article says the death toll on the island is now 80. I would guess it's quite unlikely that a single assailant could have caused so many casualties; however, the article doesn't speculate on that. Whether Norway's participation both in the NATO operation in Libya and in ISAF (Afghanistan) was part of the motive for the attacks remains to be determined.