This is a pretty annoying issue. China also shows the same issue, as well as germany. Sweden too in WW2 (Finland is axis, Sweden is neutral with allied vehicles).
Best approach is making matchmaking rely on subtrees - west germany, italy, taiwan, sweden go to allies; mainland, east germany, hungary and finland go to axis(finland), warsaw (rest).
It’d also help improve sim if we could add the same logic there (you can only use vehicles within the permitted subtree).