`minArmiesToMove` is just to avoid its computation from the armies engaged and to also to be explicit about it. If finally you don't need in UI, we'll remove it.

The calculation is right because with a maximum of 3 armies engaged, it's impossible to conquered a country with loss. If the attacker has loss, then defender has as much remaining armies.
```Dart
defender.remainingArmies = game.countries[defender.country].armies - defenderLoss;
```