
http://www.oecd-ilibrary.org/docserver/download/5jlv2jhfnt48-en.pdf?expires=1494939516&id=id&accname=guest&checksum=08592067325A17BFB82AC6F6E15110B2

https://www.brookings.edu/blog/up-front/2018/07/12/as-trump-twists-natos-arm-lets-run-the-math-on-defense-spending/?utm_campaign=Brookings%20Brief&utm_source=hs_email&utm_medium=email&utm_content=64421876

https://www.devcommittee.org/sites/dc/files/download/Documents/2023-03/Final_DC2023-0002%20evolution%20paper.pdf