The Dynamics of Enlargement in International Organizations

Most international organizations (IOs) expand their membership over the course of their lifespan. Although these enlargements tend to be heralded as normatively positive — for the IOs themselves, for the new members, and for cooperative outcomes more generally — expansions can also lead to conflicts in the organization. What conditions lead to enlargement rounds that reshape an organization in unexpected ways? We argue that, depending upon the diversity of the initial group of countries, members may vote to admit new entrants that can tilt organizational decision-making in unexpected directions. We anticipate fewer enlargements with lesser impact on the character of the organization among organizations that have either a smaller range of founding members or a relatively even initial dispersion. We develop an agent-based model that accounts for the complex decision-making environment and social dynamics that typify IO accession processes. The model helps us explain how the nature of decision-making in organizations can shift following enlargement, likely changing the organization’s output and goals.