The following is the April 6, 2021 Congressional Research Service report, Japan-U.S. Relations: Issues for Congress.
From the report
Japan is a significant partner of the United States in a number of foreign policy areas, including addressing regional security concerns, which range from hedging against Chinese military modernization to countering threats from North Korea. The U.S.-Japan military alliance, formed in 1952, grants the U.S. military the right to base U.S. troops—currently around...
https://news.usni.org/2021/04/09/report-to-congress-on-japan-u-s-relations