Partners and rivals? The AIIB's cooperation with preexisting multilateral development banks

The Asian Infrastructure Investment Bank (AIIB) is often seen as a challenger to established Multilateral Development Banks (MDBs) like the World Bank (WB) and the Asian Development Bank (ADB), which support the US-led liberal international order. However, project-level data reveals that the AIIB cooperates with these MDBs far more than previously recognized. Approximately half of its portfolio involves collaboration. Why does the AIIB choose to partner in some projects but not others? We argue that new international organizations have both functional and legitimacy-driven incentives to cooperate. Specifically, we hypothesize that the AIIB is more likely to collaborate in contexts where it (1) lacks operational experience, (2) corruption risks are high, (3) China's legitimacy is limited, and (4) China has no established development presence. Using original data on AIIB projects (2016-2023), we find that AIIB-WB cooperation is less pronounced in countries with pre-existing Belt and Road Initiative (BRI) ties to China. In contrast, AIIB-ADB cooperation increases with corruption levels and is more common in BRI-affiliated countries. Our findings contribute to better understanding how newly created institutions navigate the complexities of power transitions in the international political economy.