News U.S.A - https://www.cia.gov/library/publications/the-world-factbook/geos/us.html - https://www.cia.gov/library/publications/the-world-factbook/attachments/summaries/US-summary.pdf Vietnam - https://www.cia.gov/library/publications/the-world-factbook/geos/vm.html - https://www.cia.gov/library/publications/the-world-factbook/attachments/summaries/VM-summary.pdf