https://sipri.org/media/press-release/2018/global-military-spending-remains-high-17-trillion
https://www.visionofhumanity.org/wp-content/uploads/2024/06/GPI-2024-web.pdf
https://sipri.org/sites/default/files/2017-09/yb17-summary-eng.pdf
https://apps.dtic.mil/sti/pdfs/AD1151522.pdf