Towards the end of the First World War, he served briefly as a Captain in the United States Army, after which he returned to private enterprise.
Osborn wrote Our Plundered Planet, and when published in 1948 it became very influential in the early Environmental movement and helped spur a Malthusian revival in the 1950s and 60s.
[2] He is also remembered for being an early opponent of synthetic pesticide use, for producing several films dealing with endangered species, flood control, and water resources, as well as for his second book, The Limits of the Earth (1953), and a collection of short essays he edited under the title of Our Crowded Planet (1962).
From 1948 to 1961, he served as the first president of the Conservation Foundation, an organization he founded with several like-minded colleagues to raise awareness about ecological problems.
Upon his death in New York City on September 16, 1969, he was commemorated for his significant contributions to various conservation organizations and his proactive efforts to raise awareness about the perils of unregulated population expansion and advocate for sustainable utilization of natural resources.