When the Pacific Alliance was created in 2011, its proposal to reestablish open regionalism led to a debate on the fragmentation of regional integration and the Atlantic-Pacific divide. A decade later, Latin American regionalism is under stress, but the Pacific Alliance is not. Moreover, regionalism in South America displays features that are observed in the Pacific Alliance. From a constructivist framework, this article analyzes how the ideas from the Pacific Alliance shaped the early development of Prosur, highlighting the role of Chile, Colombia, and Peru in influencing South American regionalism. This article aims to contribute to debates on the future of Latin American regionalism by stressing how the Pacific Alliance influences regionalism, dispelling the idea that it is a mere trade bloc, and showing how it consolidates the Bogotá-Lima-Santiago axis in South American regionalism. It sheds light on the relevance of this regional bloc in political terms and on the agency capacity (achievements and limits) of Colombia, Peru, and Chile in setting a regional agenda.