Each player controls at least one stack (or is out of the game). The stack represents an Warmaster army of up to 1000 points. The army and the stack are virtually the same thing. The stack is used in  the strategic rounds on the map and the army is used for the Warmaster battles. Any change will always effect both (as they are the same thing). 

The stack is made up from an single army-marker and at least two unit-markers.

The points value  of a stack is the sum of the points values of it's unit-markers and is of course equivalent to the points value of the Warmaster army.