The Diffusion of International Environmental Agreements: The Role of Learning, Competition and Emulation

<jats:title>ABSTRACT</jats:title> <jats:p>International environmental agreements are key instruments for addressing transboundary environmental problems, but treaty ratification remains uneven and clustered across countries despite the proliferation of multilateral treaties. While existing research has concentrated largely on domestic political‐economic determinants, less is known about the role of cross‐national interdependence and strategic interactions in the ratification of treaties. To address this gap, we present a comprehensive analytical framework drawing on policy diffusion theory to assess whether and through which channels environmental treaty ratification diffuses internationally. Using static and dynamic spatial econometric models on a global panel of 140 countries over the period 1990–2018, we specifically examine learning, competition, and emulation through theoretically grounded interaction matrices that reflect one‐to‐one relationships between countries and clearly identify trade competitors, cultural peers, and learning channels. The results prove that spatial dependence and significant spatial spillover effects exist across countries. Learning and competition are dominant mechanisms, while the magnitude of the peer‐based emulation effect is weaker but statistically significant. Dynamic specifications indicate strong temporal persistence in treaty ratification, reflecting policy path dependence. Prior actions of neighbors play a significant role in shaping current decisions; early adopters act as policy laboratories. The study advances diffusion research by moving beyond distance‐only proxies and explicitly modeling cross‐national interdependence through mechanism‐specific interaction matrices, offering a stronger empirical basis for assessing how cross‐national spillover shapes IEA ratification.</jats:p>