I really tried hard to think I missed stg with Breakthroughs, but I now believe stg is .. broken
!
In all battles I played , in Serbia and Tannenberg scenarios (playing Central - I still didn't tackle the big campaigns), I never could select any regions in the breakthrough subscreen... Everything seems in order, but no amount of clicking select anything. The only time it worked was for the tutorial (but you lose the fight !)
I have checked that I was attacker, had reserves, I think weather was fine (Aug 14..), what did I miss ??


Those are your events. Each card has an icon in the middle of it representing the nature of the even (espionage, political, battle, etc.), and this icon is greyed out if you cant play it in the current phase, and black if you can. Play the battle event at the start of the battle.