Does anybody know where I can major in Music History in the US?
Beale Street.
Oberlin also has it.
You may also want to consider Kenyon’s music history offerings: https://www.kenyon.edu/academics/departments-programs/music/academic-program-requirements/requirements-for-the-major/music-history-at-kenyon/.
Search for BA programs in Musicology. This includes music history (and can usually be focused on the history aspect if that is your area of greatest interest) but is slightly more broad.
Examples:
UCLA: https://schoolofmusic.ucla.edu/academics/musicology/ba/
BU (see musicology/ethnomusicology sub-concentration) https://www.bu.edu/academics/cfa/programs/music-ba/
CU Boulder https://www.colorado.edu/music/sites/default/files/attached-files/ba-musicology_world_musics_4.pdf
SUNY Geneseo https://www.geneseo.edu/music/ba-music-musicologyhtcc-focus
(not a comprehensive list by any means, but proof of concept)