Minilateralism

Minilateralism has become the popular modus operandi of 21st-century international relations among states. As a concept, minilateralism is quite fluid. It indicates a grouping of a small number of like-minded states pursuing mutual goals. It is considered a nimble and more targeted approach than multilateralism where “the smallest possible number of countries needed to have the largest possible impact on solving a particular problem.” In contrast to the traditional multilateral system, minilateralism delivers speed, ad hoc flexibility, a level of informality, and innovative experimentalism to diplomatic initiatives.

(...) The convergence of interests and threat perceptions among states facilitate the practice of minilateralism. In other words, when the strategic priorities of states are closely allied, it paves the way for minilateral arrangements among them.  

Source: https://www.wilsoncenter.org/blog-post/multilateralism-minilateralism-regional-cooperation-trends-horn-africa