The following is the Dec. 14, 2018 Congressional Research Service report, U.S. Periods of War and Dates of
Recent Conflicts.
From the report
Many wars or conflicts in U.S. history have federally designated “periods of war,” dates marking their beginning and ending. These dates are important for qualification for certain veterans’ pension or disability benefits. Confusion can occur because beginning and ending dates for “periods of war” in many nonofficial sources are often different from those...
https://news.usni.org/2018/12/26/report-congress-u-s-periods-war