From the publisher’s website:
Three Battles of Manassas, is three games in one and covers the First Battle of Bull Run, gives a second-edition treatment of the 2nd Manassas battle (originally simulated in the CWB first edition game August Fury), and takes a “what if” look at a potential 3rd Battle of Manassas in the fall of 1863.
The large map area lets you play the full campaign of each of the three battles. There is a large amount of room to maneuver. There are also a large number of poor leaders who can refuse to move, misunderstand your orders & generally frustrate your plans.
There are options to have better leaders (like Grant, in 1862) take command.