Why do regional powers such as Brazil, South Africa, or Russia undertake different collective strategies to supply public goods in their regions of influence? When do those states prefer to delegate competences to existent multilateral financial institutions, such as regional development banks (RDBs), and when do they prefer to make use of their own national financial instruments? Why do those states create new RDBs that challenge the existing ones? The article builds and tests a set of hypotheses based on the interplay between capabilities and legitimacy to help answer these questions using contemporary South America as a case study. Through a process tracing analysis carried out for the period 2000–15, the article explains the different strategies undertaken by two states, Brazil and Venezuela, to supply infrastructure in the region, ranging from the use of the Brazilian National Development Bank to the creation of a new Bank of the South. It is suggested that the low capabilities and legitimacy expectations of both states explain the rising importance of external actors in the supply of regional public goods that we are currently witnessing in South America.