Second Cold War

The purpose of formation of Nato immediately after World War II was to provide collective security against the Soviet Union. Was there any need for this military alliance to continue even after the disintegration of the Soviet Union and collapse of the Warsaw Pact alliance? If the spirit of cooperation that was seen during the negotiations for reunification of Germany had prevailed, successive US administrations would not have been so keen on Nato's enlargement immediately after the disintegration of USSR.