While historically “Amazon” could refer to a river, a basin, and later a forest, it has been shaped into a coherent regional space by the development politics of governments, companies, and nongovernmental organizations throughout the 20th century, concealing a more complex cultural and ecological reality. Development discourses ignored the human technologies existing prior to the 16th century and drew on the imaginary of a “pristine” jungle, which actually resulted from the human depopulation that occurred in the Amazon during colonization. Colonialism (17th–19th centuries), nonetheless, connected the region to the global economy, indirectly leading to the “rubber boom” (1880–1920), when the Amazon became indispensable to the second industrial revolution. After state and business actors led different operations meant to “modernize” the region in the first half of the 20th century, “developing” the Amazon became a major target of the Brazilian government in the decades following World War II. The politics of the military regime that ruled from 1964 to 1984 in particular drove the expansion of roadways, cattle-ranching, mining, and dams. While statistically creating economic growth, this trend had disastrous consequences for nature, Indigenous livelihoods, and labor relations, which mobilized scientists, activists, and local communities against it. Yet, although by the 1990s the developmentalist model was highly contested, social and environmental movements did not manage to gather society behind a new consensus for the Amazon. Attempts to put development at the service of reducing inequalities and to reinforce environmental legislation achieved certain (mitigated) success in the early 21st century, but they did not prevent deforestation and land conflicts from trending upwards after 2015, threatening the Amazon’s very existence.