The 11 of september not only four aircrafts in the US were hijacked by al-Quaida terrorists, but also three norwegian aircrafts. The Norwegian Parlament, the Royal Castle and the Nidaros Cathedral were all destroyed just like the World Trade Center.
The reason for this were and are still unclear. A conspiracy against (or by) the norwegian oil industry and anger against the Nobel Peace Price are the most popular explanations, but intelligence agencies seems still be undecided on the cause. To attack the parlament only the day after the general election, when the parlament wasn't in session, is a sign that the Norwegian attack was secondary to the US attacks.
Hardly surprisingly Norway, after replacing its dead parlamentarians and crowning a new monarch, joined the War on Terror as a full partner. The following years saw some small terrorist attacks in Norway by immigrant muslims and the election 2005 resulted in a stronger center-right majority where the populist Progress Party joined the government.
Norway started to get highly negative publicity by joining with the US and since the war in Iraq raised the oil price, helping the Norwegian oil export. Michael Moore dedicaded half an hour of his movie
Farenhit 911 to Norway in a highly unflattering way. Naomi Kleins book
The Shock Doctrine took several examples of fascist shock tactics from Norway after 2001.
It is widely accepted that giving George W Bush the Nobel Peace Price by 2008 was both a reward for a fairly successful War on Terror, a thank from Norway to the US for past help and a finger to the global anti-war left.