Promise of International Organizational (IOs) Expansion: Rethinking the Expansion of Security IOs From a Multi-Dimensional Approach

This study investigates the multidimensional expansion patterns of international security organizations (ISOs), analyzing both horizontal (membership enlargement, geographic reach, partnerships) and vertical (mandate expansion, governance reforms, operational capacity building) dimensions of growth. Through a comparative analysis of NATO, the Shanghai Cooperation Organization (SCO), and the Collective Security Treaty Organization (CSTO), the research reveals distinct expansion trajectories shaped by geopolitical contexts and institutional designs. NATO demonstrates comprehensive expansion across both dimensions, driven by its institutional flexibility and strategic adaptation. The SCO exhibits cautious horizontal growth coupled with selective functional vertical diversification, reflecting its consensus-based model. The CSTO, constrained by its regional focus and dominant power dynamics, shows limited horizontal expansion but incremental vertical development. The findings contribute to understanding how ISOs balance external pressures with internal capacities, offering insights into their evolving roles in global security governance.