Just that she had 30k cavalry vs 20, so presumably the BB cavalry either was there to protect the infantry, in which case those could not be "easily chrushed" or they were not, in which case they would not be annihilated, only the infantry would.
I agree with BB that this was some kind of bug in the game. If you arrive with a cavarly superior army like this I can hardly believe it would be possible for you to get annihilated within a second. You might lose your moral quite fast, as might happen if your army's moral is mixed together with that of your ally. But then this only decreases the risk that you are annihilated since you will lose the battle because of moral loss before many get killed. BTW, why should your moral get mixed with a non-ally? BrB and RUS were not allies. But perhaps the game engine does not make such a distinction.
As for you being called "pretty much a liar", its bad, really bad. Were you really called that? Are your fellowgamers mentally sane individuals?
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Tonioz, was it not possible to make "trials" with some Russian battle simulator? Could one simulate a very bad dice roll for you and also feed the program with the actual stats about moral, LT, size of army, army components etc, and then see if it is at all possible to get this result? Well, perhaps also taking into consideration the dice roll of the previous battle between RUS and AUS. Coming to think about it, you mentioned that BrB somehow inherited Russia's dice roll. And that may well be the core of the problem. Assume that this dice roll was made when RUS had say 5000k left and AUS 30k and a great cavalry advantage for AUS - a total annihilation situation presuming a good dice roll. After it has been put into effect the BrB army wanders into the battle and instead of getting a dice roll of their own and a combat resolution table of their own etc inherits all of Russia's and thus get annihilated themselves. Well, then to me it is a clearcut bug. The game engine did not take the BrB army into consideration when calculating the outcome of the battle. But it was present on the battlefield.