Burden Sharing: Benefits and Costs Associated with the U.S. Military Presence in Japan and South Korea, Report to Congressional Committees [open pdf - 2MB]
From the Highlights: "Both DOD and the Department of State (State) report that cooperation between the U.S. and its allies Japan and South Korea is essential for confronting regional and global challenges. The decades-long forward presence of the U.S. military in those countries has undergirded these security alliances. DOD has about 55,000 troops in Japan, its largest forward-deployed force in the world. DOD has about 28,500 troops in South Korea. It spends billions of dollars annually and maintains dozens of facilities in both countries, ranging from tens of thousands of acres for training sites to single antenna outposts, in support of this presence. The National Defense Authorization Act for Fiscal Year 2020 included a provision for GAO [Government Accountability Office] to report on the security benefits derived from the forward presence of the U.S. military in Japan and South Korea and the costs associated with it for calendar years 2016 through 2019. This report describes (1) the identified benefits to U.S. national and regional security derived from the U.S. military presence in Japan and South Korea, (2) the funds obligated by the U.S. military for its presence in Japan and South Korea for 2016 through 2019, and (3) the direct and indirect burden sharing contributions made by Japan and South Korea for 2016 through 2019."
Government Accountability Office: https://www.gao.gov/