To be sure, a military alliance can serve additional purposes, and NATO played a role in fostering democracy in its members. But other international institutions can also serve that purpose. As NATO's role in Bosnia reminds us, the distinctive features of a military alliance are its war-fighting capabilities and responsibilities. Fear of Russia Since the purpose of a military alliance is to deter and fight wars, the countries that want to join the alliance typically have a particular threat in mind. Alliances are different from collective security systems.
Collective security is designed to be inclusive.
Any country can join, and any country, even a member, can become an enemy that must then be disciplined by the other members. As noted, the United Nations was designed as a collective security system. After the Cold War ended and Iraq invaded Kuwait, the United Nations authorized military action against Iraq even though it was a UN member. Alliances are very different. Unlike collective security systems, they are exclusive, because they have a particular enemy in mind.