The North Atlantic Treaty Organization's original purpose was a the shared defense of Western Europe against the Soviet Union. Although not part of Europe, the US, with its large military and anti-Soviet stance, played a major role in the establishment of NATO.
Note to Mike109: NATO is now and has never been part of the United Nations. It is a completely separate multilateral organization that has at times taken positions contradictory to those of the UN. [Given that the former USSR had veto power in the UN Security Council, that was bound to be the case!.]