https://www.bruegel.org/wp-content/uploads/2021/09/PC-2021-18-0909.pdf
https://www.eppgroup.eu/download/file/t5F7fWVHAho9XFLF3fGb3HMHOc_fBpiq-JJIhg_2alGxibc6qNgf4Xn7KKgAAAACEQU0OTEyMw
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://economy-finance.ec.europa.eu/document/download/f5827354-8501-49cb-bf2d-13f2f7a9444f_en?filename=dp199_en.pdf