Originally posted by Steel
There's been several comments from Max and Vulture on this, to para-phrase "the AI does not handle low manpower well". This is based on Paradox beta feedback. Something to keep in mind as this would potentially change game balance a lot and potentially break the AI countries even more.
No one talks about making their mapower level and grow zero (well, ghost talks about that, not I

).
In case of Romania, Hungary and Bulgaria lowering units output got good expaination - they simply were not as much in the war as HoI implies (especially Bulgaria). And we are not able to simulate properly their work as a garrison forces in Yugoslavia.
From those countires only Romania was serious frontline force (2 armies send on the Eastern Front), Hungary had much less troops. And right now even Vichy sends corps size units as a support...
Other idea - does the rise (really high rise) of garrison pririority (vs front) in AI lowers amount of units send as a expeditionary force? Not sure about that how exactly AI decides, thet it can send some troops to it's ally, but if they are taken only from "front" pool, then rising garrison levels might help in keeping those Axis minors at home.