In international relations, multilateralism is a kind of alliance where multiple countries progress any given goal.
Multilateralism was defined by Miles Kahler as "international governance" or global governance of the "many," and its central principle was "opposition [of] bilateral discriminatory arrangements that were believed to enhance the leverage of the powerful over the weak and to increase international conflict". In 1990, Robert Keohane simply defined multilateralism as "the practice of coordinating national policies in groups of three or more states.John Ruggie further elaborated the concept of multilateralism based on the principles of "indivisibility" and "diffuse reciprocity (international relations)" as "an institutional form which coordinates relations among three or more states on the basis of 'generalized' principles of conduct ... which specify appropriate conduct for a class of actions, without regard to particularistic interests of the parties or the strategic exigencies that may exist in any occurrence."
Multilateralism, whether in the form of membership in international institutions, serves to bind the great power, discourage unilateralism, and give the small powers a voice and voting opportunities that they would not otherwise have. Especially, if control is sought by a small power over a great power, then the Lilliputian strategy of small countries achieving control by collectively binding the great power is likely to be most effective. Similarly, if control is sought by a great power over another great power, then multilateral controls may be most useful. The great power could seek control through bilateral ties, but this would be costly; it also would require bargaining and compromise with the other great power. Embedding the target state in a multilateral alliance reduces the costs borne by the power seeking control, but it also offers the same binding benefits of the Lilliputian strategy. Furthermore, if a small power seeks control over another small power, multilateralism may be the only choice, because small powers rarely have the resources to exert control on their own. As such, power disparities are accommodated to the weaker states by having more predictable bigger states and means to achieve control through collective action. Powerful states also buy into multilateral agreements by writing the rules and having privileges such as veto power and special status.