Ostertag became an expert on the political crisis in Central America and published widely for a diverse range of publications, including Pensamiento Propio (Nicaragua) Pensamiento Critico (Puerto Rico), The Guardian (London), the Weekly Mail (South Africa), Mother Jones and the NACLA Report on the Americas (US), AMPO (Japan), and even the clandestine theoretical journal of the New People's Army in the Philippines. He alternated his time in Central America with organizing and public speaking in the US, giving lectures at Harvard, Yale, Princeton, Rutgers, and many other schools and institutions.