Basically if I went out to war and I had a buddy of like mind and like scope we could cooperate together and work as one man in a fight. In Empires and Generals we call this Banding.
Banding works this way:
You have a unit (Soldier, General, Philosopher, etc...) that does not specifically tell you that he cannot be banded to, you have another card that says in its Effects or Abilities that he CAN band to that other card, and you place them together as one, one overlapping the other. Preferably the primary card (the main card being banded to) stays on top, but it you have room you can do it however you wish.
It is imperative that everyone knows who is banding to whom.
Sometimes there are cards that let them "band together". And this is fine, but, just as in real life, if you place two equal men in a room - one will lead the other eventually. And so it is with banding. There is the one card that is BANDED TO and the one card that is BANDING. Or many cards, in the case of The Huns Horde cards.
So if I played a Tactics Card that read: "Every unit in play that banded to another is discarded". The secondary card(s) would be discarded, whereas if I played an Ability that said: "Every Unit that is banded to is Unbanded and the card that was banded to is discarded"... I would discard the primary card.
The glossary defines it as this:
Band - Combines the given attack numbers as well as the defense. Two 5/5 banded Soldiers are treated as one 10/10 Unit. This can be done at the War Camp or the Battlefield only during Army Phase. At first glimpse there may seem to be two different types of banding: "Band with" and "Band to". This is incorrect. In every group there is always a small group leader. Banding takes place when one card bands itself to another. There is always a primary or a chief target that is banded to in every unit.