Revised, the minimum bid I would take for germany was an infantry in ukraine, though I preferred minimum artillery for libya.
AA50, I guess it’d be an infantry in egypt… lowest I recall, but I really did not feel like playing axis that day.
I played V4 a few times without bid… prefer revised rules.
Classic I prefer original classic rules, but I do attack karelia round 1 (guys stranded in norway so may as well take a stab at karelia)… I think 10 was the lowest I went. Man been awhile since I played classic.
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I have taken allies at 0 against newer opponents and won. Same for AA50 when it first came out. Revised rules same thing when it first came out.
The bid system takes time to flesh out. I believe in 1 unit per territory, also 1-9 is relatively small enough that you could play with or without it.
For all A&A games I prefer to play with a bid or against an opponent who takes a bid. It changes the game up.