A confederation (also known as a confederacy or league) is a union of sovereign groups or states united for purposes of common action. Usually created by a treaty, confederations of states tend to be established for dealing with critical issues, such as defense, foreign relations, internal trade or currency, with the central government being required to provide support for all its members. Confederalism represents a main form of intergovernmentalism, which is defined as any form of interaction around states which takes place on the basis of sovereign independence or government.