The international community has consistently emphasized the importance of protecting the Amazon rainforest as a global carbon reservoir and climate regulator. Basin states have historically responded by rejecting the ‘internationalization of the Amazon’, arguing that they have sovereign rights to exploit the area under their own development plans. By reaffirming their sovereignty rights over international environmental concerns, they have also excluded the ancestral rights of Indigenous peoples in the basin. This article examines how the principles of absolute sovereignty (‘enclosure’), ‘common heritage of humankind’, and ‘common concern of humankind’ have been incorporated into the discourses, instruments, and practices of international environmental governance of the Amazon. These principles interact through shared anthropocentric, ethnocentric, and state-centric premises. Through an analysis of the Amazon Cooperation Treaty Organization (ACTO), the article finds that despite the discursive rejection of international forces, the basin states appeal to ‘common concern’ to embrace international cooperation while promoting transnational extractive and infrastructure projects through the principle of ‘enclosure’. This produces fragmented governance that legitimizes the expansion of extractivism under sovereign and developmental imaginaries while excluding the self-determination claims and ecological perspectives of the Indigenous peoples of the Amazon.