A determinate region within which a single external power exercises a predominant influence, limiting the political independence of weaker states or entities within it. The concept plays a central role in the analysis of imperialism and Great Power politics. Definitions and discussions of spheres of influence revolve around three dimensions. The first concerns the nature and scope of the imposed limits—whether the dominant power seeks to control only the foreign policies of weaker states or its domestic economic and political arrangements. Whilst different from formal empire which involves direct control and administration, the concept is often closely tied to notions of informal empire and to the concept of hegemony. The second dimension concerns the character of the power relationship, including the types of power involved (coercive, institutional, ideational) and the degree to which influence involves the active cooperation of elites or groups within the subordinate state (whether pro‐US militaries in Latin America or local communist parties in Eastern Europe during the Cold War). The third dimension concerns the degree to which spheres of influence are recognized by other states or by international society more generally. This might involve formal agreement amongst particular states on the creation of spheres of influences—as in the practices of European imperialism in the period following the Conference of Berlin (1884–5), with the 1907 Anglo‐Russian convention concerning Persia providing a very clear example. Or it might involve the attempt by a state to secure formal legal recognition of its sphere of influence, as in the failed attempt by the US to secure inclusion of the Monroe Doctrine in the Covenant of the League of Nations or Churchill's proposals for ‘regional policemen’. Finally, and most importantly, spheres of influence may be embodied in the informal political norms that emerge as part of major power rivalry—as with the tacit understandings regarding the position of the US role in the western hemisphere or of the USSR in Eastern Europe and now Russia in its ‘near abroad’.