Norway is not a member of NATO, so it has not left the alliance. However, Norway is a member of NATO’s Partnership for Peace program and has been a close partner of the alliance since the end of the Cold War. Therefore, the question of why Norway would leave NATO may be better rephrased as “Why would Norway choose not to join NATO?”.

Norway’s relationship with NATO has been shaped by a variety of factors, including its geography, history, and politics. Here are some of the key reasons why Norway has not joined NATO:
Neutrality: Norway has a long tradition of neutrality in international affairs. During the Cold War, Norway pursued a policy of “non-alignment”, which meant that it did not align itself with either NATO or the Soviet Union. This policy was designed to ensure Norway’s security and independence in a polarized world. Even after the end of the Cold War, Norway has been reluctant to join NATO, as it sees itself as a bridge-builder and mediator in international conflicts.
Strategic ambiguity: Although Norway is not a member of NATO, it has a close relationship with the alliance and has cooperated on a wide range of issues, including military exercises, intelligence-sharing, and peacekeeping. This strategic ambiguity allows Norway to benefit from NATO’s security guarantees while maintaining its independence and flexibility in foreign policy.
Public opinion: Public opinion in Norway has been divided on the issue of NATO membership. Some Norwegians view NATO as a necessary bulwark against Russian aggression, while others see it as a provocative and destabilizing force. In recent years, there has been growing concern in Norway about the risks of a new Cold War with Russia, which has led some to question whether NATO membership would make Norway more secure or less secure.
Geopolitics: Norway’s location on the northern flank of Europe makes it strategically important for NATO, as it provides a gateway to the Arctic and the North Atlantic. However, this also makes Norway vulnerable to Russian pressure and influence, which has led some Norwegians to question whether closer ties with NATO would exacerbate tensions with Russia.
In conclusion, Norway has not left NATO because it was never a member of the alliance in the first place. Norway has chosen not to join NATO for a variety of reasons, including its tradition of neutrality, strategic ambiguity, public opinion, and geopolitics. While Norway has cooperated closely with NATO on a range of issues, it has maintained its independence and flexibility in foreign policy by not joining the alliance.