The correct answer is - to act as a treaty of friendship among the Soviet Union and the other Eastern European countries.
NATO is a military organization. It has been formed as an alliance which was supposed to protect the interests and the territories of the member countries, such as the USA, UK, France, Canada, Australia, and oppose the Soviet Union and the Warsaw Pact alliance.
After the fall of the Soviet Union, NATO lost its primary reason for its existence, but it turned into other directions. It started to act as a world peace-keeper, at least in its own ways, because looking at the facts suggests that the organization has initiated more conflicts and wars than it actually managed to prevent or stop.
