The central puzzle is that regional organizations can produce three outcomes rather than a simple continuum between weak cooperation and supranational integration. Some remain loosely coordinated, some transfer authority to supranational institutions, and some sustain a working division of labor among sovereign states. Traditional functionalist accounts mainly address spillover from technical cooperation into political integration, while realist approaches emphasize competition, liberal theories explain why cooperation begins, and role theory addresses how national identities shape behavior. Remaining Spaces Theory, by contrast, asks how hierarchy generates functional differentiation after cooperation already exists. Its proposed sequence is Primary Space Occupation → Structural Constraint → Innovation → Deep Specialization → Functional Role Differentiation → Polycentric Network. A primary space is a bloc’s most visible and consequential strategic domain, often political leadership or military predominance, while a remaining space is a function left underdeveloped, politically constrained or insufficiently served by other members.

The framework identifies a domain as a remaining space when the dominant member has made no sustained state-directed investment in it, no other member has consolidated a dominant position, and demand for the function remains unmet. These spaces are not fixed: technological change can create new domains, geopolitical shifts can alter their value, and expansion by the primary power can close one space while opening another. A niche is the function a state selects; specialization is the deepening of capability in that function; a functional role is the resulting position within the regional division of labor; and systemic relevance is the degree to which other actors depend on it. Multiple states may initially occupy the same space, but the theory predicts that sustained, undifferentiated co-occupation is unstable. Under this formulation, specialization is relational rather than a direct expression of comparative advantage: states with similar endowments may fill different roles when they operate within differently configured regional hierarchies.

Remaining Spaces Theory also distinguishes structural opportunity from political agency. Occupation by a leading member constrains secondary states by making direct competition there costly and potentially disruptive to the cooperative framework, but it does not mechanically compel specialization. Sovereign governments still choose whether to fill an available function, attempt to replicate the leader’s role or leave the space unused. The theory is expected to operate under five conditions: an existing cooperative framework, a recognized power hierarchy, shared interests that make positive-sum outcomes preferable to rivalry, a period of growth or systemic change that supplies resources for investment, and sufficient structural trust that the regional arrangement is considered worth preserving. Structural trust refers to confidence in preserving the regional system, whereas tactical trust concerns confidence between particular states on particular policies. The theory does not require a central institution to allocate functions, and it also predicts a different response where hierarchy is absent: competitive emulation may be rational because no position has been decisively closed.

The Gulf Cooperation Council provides the study’s most detailed process-tracing case. Saudi Arabia is treated as the primary-space occupant because of its demographic weight, economic scale, political centrality, hosting of the GCC Secretariat in Riyadh, participation in the G20 and leadership of OPEC+, among other indicators. Rather than competing in that political-strategic domain, other members developed distinct functions. The United Arab Emirates concentrated on logistics, finance and global connectivity through Jebel Ali Port, Dubai International Airport, the Dubai International Financial Centre and Abu Dhabi Global Market. Qatar emphasized diplomatic mediation and maintained channels with actors including the United States, Iran, Israel and Hamas. Kuwait drew on its development-finance institution to build a humanitarian role, Oman developed a reputation for discreet backchannel facilitation, and Bahrain combined security hosting with Islamic-finance and financial regulation. No GCC summit or treaty formally assigned these roles, an observation the author uses to distinguish structural adaptation from institutional delegation.

The Gulf case also illustrates how differentiation changes when an occupied space is contested. Bahrain initially sought to become the bloc’s principal financial hub, but Dubai entered the same domain with greater resources and displaced that position; Bahrain subsequently concentrated on Islamic finance and fintech regulation, where it could build a more distinct niche. The pattern is presented as a “displacement test” of the theory: when a secondary state encounters a more capable occupant, it may iterate toward deeper specialization rather than continue direct competition. The 2017 Gulf crisis does not appear to have dissolved the wider functional architecture, which the author interprets through the distinction between damaged tactical trust and surviving structural trust. At the same time, emerging competition between Saudi Arabia and the United Arab Emirates in tourism, technology and foreign investment shows that specializations are not permanent. Their expansion can compress the opportunity space and force reassessment, meaning that the proposed outcome is dynamic reconfiguration rather than a stable equilibrium.

The European Union serves as a high-differentiation comparative probe with much denser institutions. Germany occupies a primary economic space through industrial scale, export dominance and eurozone leadership, while France occupies a complementary diplomatic and military space through its United Nations Security Council seat, nuclear capability and historical role in European foreign policy. Other members developed roles that the study associates with spaces left open by this Franco-German axis. Ireland became a technology and corporate-tax hub after the single market removed barriers to mobile investment; Luxembourg specialized in investment funds and securities infrastructure after the 1985 UCITS directive; the Netherlands used Rotterdam and Schiphol to become a logistical gateway; and Sweden and Denmark built positions in environmental, humanitarian and normative policy. Unlike the GCC, these roles are embedded in a single market, common regulation and supranational institutions, which may reinforce them even if institutional allocation is not their original cause.

ASEAN and the African Union test the framework’s boundary conditions. Indonesia is the largest ASEAN economy and hosts the bloc’s Secretariat, but its authority is limited by the comparable weight of Thailand, Vietnam, the Philippines and other members, leaving hierarchy contested. Several states consequently pursue overlapping strategies in manufacturing, export processing and international tourism, producing competitive replication rather than a stable complementary division. Singapore is the conspicuous exception: its small scale and distinctive city-state economy channel it toward logistics, finance and business regulation, creating capabilities that other members rely on. In the African Union, South Africa, Nigeria, Egypt, Kenya and Ethiopia all contest leadership, and no state has consolidated the primary space. Although individual achievements exist—such as Kenya’s mobile-finance platform and Rwanda’s governance reputation—the study finds little continent-wide systemic dependence on specialized member-state roles. The AU also assigns some functions, including mediation, to standing organs, but the author argues that this does not explain the broader pattern because logistics, finance and technology likewise lack a coordinated state-level division of labor.

Across the four cases, the paper interprets the findings as evidence for a third regional-order model between hierarchy and balance-of-power rivalry: a polycentric network in which influence is distributed across functional nodes. The EU and Gulf Council are the strongest cases, ASEAN provides partial differentiation and the AU exhibits little. The comparison is designed to challenge four alternatives. Comparative advantage cannot fully explain why Bahrain repositioned after Dubai’s advance; hegemonic imposition is inconsistent with the absence of GCC role assignments; institutional delegation cannot be necessary because differentiation appears in the minimally institutionalized Gulf; and status competition does not readily explain why secondary states systematically avoid the leader’s core domain. The design nevertheless has important limits. Only the GCC receives full process tracing, systemic relevance is assessed through counterfactual judgments about disruption rather than direct measurement, and the framework does not specify which particular space a state will choose or whether an available niche will ultimately be consequential.

Future work would need to test the theory more systematically rather than treating the four blocs as decisive proof. The author proposes developing quantitative indices of role specialization, potentially using concentration measures for economic, logistical and diplomatic activity, and examining whether differentiation predicts growth, crisis response or conflict management. A larger sample could also distinguish the proposed mechanism from institutional design, comparative advantage and status competition more rigorously, while network measures of intra-bloc trade and diplomatic flows could make “systemic relevance” measurable. Extending the idea beyond regional organizations is speculative but testable: in a fragmented international system, middle powers may face an analogous constraint when great powers occupy prominent diplomatic or security domains, potentially encouraging specialization in climate finance, maritime corridors or other neglected functions. The paper’s central claim is therefore not that hierarchy invariably produces healthy cooperation, but that hierarchy can channel sovereign states toward distinct roles, creating a resilient regional system without requiring either centralized authority or identical strategies.

Subject of Research: How regional power hierarchies shape functional specialization among sovereign states

Article Title: Remaining Spaces Theory: explaining functional role differentiation in regional blocs

Article References: Alhajri, A. M. S. H. H. (2026). Remaining Spaces Theory: explaining functional role differentiation in regional blocs. Frontiers in Political Science, 8, Article 1895288. https://doi.org/10.3389/fpos.2026.1895288

Image Credits: AI Generated

DOI: 10.3389/fpos.2026.1895288

Keywords: regional blocs, functional differentiation, power hierarchy, middle powers, niche diplomacy, polycentric order, Gulf Cooperation Council, European Union, ASEAN, African Union, Remaining, Spaces