The North Atlantic Treaty Organization is a mutual defense alliance which stated that it would give support to any member who was attacked. It was formed after the Soviets started the Berlin blockade and convinced Americans that the USSR wanted to become a superpower. Initially, it included 12 countries: the USA, Canada, Britain, France, Italy, Belgium, Denmark, Portugal, the Netherlands, Norway, Luxembourg, and Iceland. It was a significant point in the Cold War because it intensified the threat that the Soviets felt from western Europe. They responded by creating the Warsaw Pact among communist countries. The Cold War now had two distinct sides which the war was being fought from. Countries had to officially pledge their allegiance to one side.