Designating a target

[Sociopsychoactive]

It's hidden on the diplomacy main screen. Before you select any factions, look on the bottom left of the diplomacy screen and one of the buttons there is 'designate target'. Hit it then select something on the map and your allies will flail around innefectually before launching a poorly chosen stack of unsuitable units in the vague direction of it who will then position themselves to completely fail to support your armies, and when you finally do manage to get them to come along as re-inforcements they will throw themselves at the enemy with reckless abandon long before your army gets into position, leaving you to fight them as if they weren't there at all.

At least thats what happened to me every time.