The study of all the different aspects of changes in the population structure, along with its increase or decrease, is accompanied by factors.The macro trends affecting the age structure of the country's population include sub-trends with numerous effects and consequences that are beyond the control and will of the role-players.The macro trends, influenced by key factors and drivers in the population area, are able to bring about extensive changes in the population structure.The present study aims to determine the macro trends and environmental trends, key factors and drivers affecting changes in the age structure of the population of the Islamic Republic of Iran, with an emphasis on military defense.This study is descriptive-analytical in terms of research method, and after receiving the opinion of the statistical population (30 people), the data were analyzed and the final result was obtained.The research findings show that three environmental macro-trends including: "economic changes", "cultural changes" and "social changes", with four key factors of mortality, migration, infertility and population development policies and programs, along with three drivers of cognitive warfare, technology and lifestyle, will affect the age structure of the country's population with an emphasis on military defense, and as a result, the country will face a significant population decline.
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