·         ALLIANCES among nations are often formed for mutual economic, political or security benefit, and can be   multilateral  or   bilateral . The North Atlantic  Treaty  Organization (NATO) was formed in 1949 to serve as a bulwark against threats by the communist Warsaw Pact in Eastern Europe. Since the fall of the Berlin Wall in 1989 and the dissolution of Pact nations, many Eastern European nations have joined NATO, thus changing and expanding its defensive outlook. A   bilateral  example is the US-South Korea Mutual Defense  Treaty  of 1953.