
https://reutersinstitute.politics.ox.ac.uk/sites/default/files/2020-06/DNR_2020_FINAL.pdf

https://www.brookings.edu/blog/order-from-chaos/2021/03/30/the-us-military-must-plan-for-encounters-with-private-military-companies/?utm_campaign=Brookings%20Brief&utm_medium=email&utm_content=118778216&utm_source=hs_email

https://deliverypdf.ssrn.com/delivery.php?ID=311071073029064107081106000088122120035055026027031023101089114109004122092126125009003043120052118045043115122093122090125016013080071041077125098094010078021014089007006008095097069030010030120071096073064079068008005002094092111071089019104067112068&EXT=pdf&INDEX=TRUE