Ethnographers concerned with Indigenous thought have called for the radical acceptance of other ontologies. This move—which echoes the increasing acceptance amongst philosophers of science that different and multiple worlds might coexist—has been referred to as “the ontological turn.” Combining the ontological turn in anthropology with the world-ecological approach to capitalism and the counter-hegemonic theory of Antonio Gramsci, this research project explores how ontologies expressed through radical environmental protests challenge the hegemonic ontology based on a Cartesian division of nature and culture. The worldmaking of Witsuwit’en waterprotectors opposing pipelines in British Colombia is studied next to that of the non-indigenous Hambach forest movement against lignite mining, a camp-based anti-fossil fuel movement in Germany. The multi-sited approach, based on the extended case method, explores how localized projects of worldmaking at environmental protest camps challenge the ontologies that gave rise to—and continue to underpin—capitalist modernity. The guiding questions are: How might the practices and narratives of radical environmental movements create a world where the facts underpinning their claims can survive? How is an ontology of human-nature entanglement constructed as a reaction to a modernist ontology of dualisms? The challenge of radical environmental movements goes beyond a physical blockade; it implies a challenge to capitalist worldmaking.