I just left active-duty this past summer. Most of the bases I've either been stationed at, or have visited have been guarded at least partially by civilian contractors. That's not necessarily true internationally, but it seems to be true at the domestic bases, and has been true since the military draw-down of the early '90s.
you’re correct...nearly all the bases and posts have civilian guards at the gates. The drawdowns plus the ongoing ops tempos with ongoing wars overseas and other military engagements have pulled the security forces personnel off the CONUS bases and pushed ‘em overseas.
Sigh...my heart is heavy today as I watch the memorial service from Ft Hood.
I’m at one of the biggest Navy base on the West coast and the entrance security is guarded by the civilian police. We also have the service guards armed to the teeth with armored vehicles patrolling the periphery because they are responsible for “other” sensitive materials :)