This is not intended to be a critiqued comparison but merely list of the differences between the two game systems.  Bother were developed by John Tiller but the Talonsoft Battleground series of games are much older and are now sold by Matrix.  The differences between the games are more than just a reflection of the progress of computers and game design.  The Battleground games are focused on presenting the battle subject as scenarios showing various historic and what if situations.  The HPS games include the historic and what if scenarios but their primary focus is to link the scenarios together as a campaign; therefore the naming "Campaign Gettysburg" etc.  This change in focus altered the design of the game system in significant ways.  So first some general observations.

Talonsoft Battleground Games

These games were released with each targeting a very specific battle like Gettysburg, Shiloh, Bull Run, etc.  This limited the subject that the game had to handle and more importantly limited the size of the map to the historic area of the battle.  This allowed the use of hand drawn maps.  There is no comparison between the quality and detail in Battleground maps as compared to HPS maps.  I'll go into the reasons when I discuss the HPS games.  All other aspects of the game like units are very similar because they are rendered by the same methods.  The mechanics of how the Battleground games render combat are based on the systems used in early board games on the same subject matter by SPI and Avalon Hill.  They use a table look up for resolving combat with table shifts to modify the combat for various effects like rear fire, etc.  This means that firing a unit singly versus as a stack can have significant impact on the outcome due to where the combat factors might fall on the table lookup.  Units take loses in steps similar to how the old board games used "chits" to mark losses.

While difficult to create the maps Talonsoft did include editors within some of their releases that allowed you to create your own maps and also create scenarios based off any of the maps.  This has resulted in almost every major Civil War battle being covered at our ACWGC Design site.  You can down load modules for the Battleground series for just about anything or develop your own.

HPS Campaign Series Games

The biggest concept change when going to the HPS games is the focus of the system away from single scenario to a chain of scenarios linked together as part of a Campaign.  To do this required HPS to include very large maps with the ability to subdivide them into smaller maps for individual scenarios.  And the number of scenarios, usually like what if ones, increased dramatically.  To handle this they went to a system of defining the map mathematically and loading about six different graphics for each type of terrain to be displayed.  This limits the range of graphics that can be displayed as part of the map.  Each hex is no long a unique graphic like in the Talonsoft version.  This allowed them to develop hundreds of scenarios to make the Campaign chain from but they lost the graphic quality of the hand drawn maps.

HPS did include a scenario editor in their games so you can create new scenarios for the system.  However, they locked the game after version 1.01 of Corinth was released so that the players can't change either the OOB or Map used in the games.  You can create your own OOB's and Maps for the Corinth 1.01 game but you are locked into its rule set.  There are a wide range of games covering other battles of the Civil War on the ACWGC Design site using Corinth engine.  Also, while it isn't possible to use hand drawn maps, there are a number of better looking terrain and unit graphic sets out there that look better than HPS's releases.

HPS also made a major change in the combat mechanics of the game.  It is now based on linear factors rather than a table.  This means if you fire 100 men twice you will get on average the same result as firing 200 men once.  Modifiers are no long table shifts but percentage changes.  Casualties and fatigue are now tracked by numbers rather than levels.  HPS also introduced a new alternate combat system to phased play called Turn play.  Turn play allows the player to combine movement and combat in one continuous play.  The Talonsoft games can only use phased play with movement separated from combat.  Turn play has a significant impact on multiplayer games because it reduces the number of mailings required for a game.

Now for a Comparison of the two Systems:

Item	Battleground	HPS
Scale	125 yards to a hex	125 yards to a hex
Turns	Uses Phased play consisting of Move, Defensive Fire, Offensive Fire and Melee	Uses Phased play consisting of Move, Defensive Fire, Offensive Fire and Melee
		Also has Turn play consisting of combined move, fire and melee or optional two phased play consisting of move and fire followed by separate melee phase.  Defensive fire handled as opportunity fire.
PBEM	Requires four emails per turn for Side 1 Move, Side 2 Def Fire, Side 1 Off and Melee, Side 2 Move, Side 1 Def, Side 2 Off and Melee.	Phased play can use AI directed Defensive Fire so requires only two emails per turn.  Turn play requires only two emails.
Formations	Line, column, limbered, mounted	Added skirmisher
Units	Infantry, cavalry, artillery, wagons, leaders, gunboats	Same
Unit Quality	A-F (best to worse)	Same
Unit states	Disrupted, Routed	Same
Fatigue	Levels 0-9 with three affect levels Fatigue loss taken in steps levels	Levels 0-999 with three affect levels Fatigue loss taken in numeric amounts
Casualties	Step losses of 25 men	Man for man losses
Weapons	About 12 types	Over 20 defined.
Artillery Ammo	Step use with one per unit	Ammo used on per gun bases
Small Arms Ammo	Wagons have step resupply, one supply strength per ammo depletion removed	Wagons have supply points where one point can resupply 10 men.
Special Terrain Features	Breastworks can be made	Breastworks can be made, also has set features like Abatis, Entrenchments, Bridges
Special Bridge Handling	None	Can destroy and repair
Special Artillery Handling	Recrew	Recrew, Spike, capture, retire by prolonge
Special Night Rules	None	Fatigue penalties for movement and melee.
Animations and Graphics	You can have short videos of re-enactors display during combat.  If you watch closely my brother is the right most man in one of the lines.

 

Since the major difference between the two systems is how combat is resolved I thought I would show you an example of how Melee is resolved in both systems.  Fire combat is done similarly but using different factors and isn't resolved as stacks in both systems.

The melee situation is a 175 man class "C" unit attacking a 125 man class "B" unit with no other modifiers.  I am using 25 man increments to conform to Battleground strengths.  In HPS this could have been 174 men attacking 123.

Battleground

Melee is by table lookup using the differential between attacker and defender.  This is obtained by dividing the strength by 100 and rounding down.  This would give:

Attacker:  175/100 = 1.75 which is rounded to 1
Defender:  125/100 = 1.25 which is rounded to 1
Differential = Attacker's - Defender's = 1 - 1 = 0

Because the Defender is a class B unit it gets a -1 modifier or table shift changing the Differential to 0 - 1 = -1
The table look up for a Differential of -1 results in a 8% chance of winning the melee.  The kill ratio for this Differential is 0.3 (Def/Atk losses).  The typical Attacker loss is 100.  This means the typical combat result will be the Defender losing 25 (one step) and the Attacker losing 100 (four steps) since there is no in between result of 30.  Both sides will take a one step fatigue loss and the attacker will take an additional step loss for losing.

HPS

HPS uses a random number generated between a Low Combat Value (LCV) and a High Combat Value (HCV) calculated for both sides.  The winner is the one with the lowest losses.  For the attacker the LCV and HCV are 50 and 200.  For the Defender they are 25 and 125 before modifiers.  These values are relative to a 1000 man unit.  As you can see from comparing these base numbers an attacker has to have about twice the numbers of a defender to get a 50:50 chance of winning.

Attacker multiplier is:  strength / 1000 = 175/1000 = 0.175
Defender multiplier is:  strength / 1000 = 125/1000 = 0.125

The Defender get a modifier for being a class "B" unit.  In HPS this is a percentage change.  In the case of quality the modifier is 10%.  This will change the 0.125 factor to  0.1375.  In addition the winner gets a random amount of fatigue equal to 1.5x to 4.5x their losses.  The loser suffers twice as much (3x to 9x) fatigue.  Applying these factors to the LCV and HCV will give the following range of results to which I have added the equivalent from the Battleground calculation:

HPS	LCV	HCV	Median	Fatigue		Battleground	Typical	Fatigue in HPS value
Attacker	9	35	22	132		Attacker	100	200
Defender	3	17	10	30		Defender	25	100

 

As you can see the results are quite different.  Battleground tends to be much bloodier in terms of number of casualties and the units tend to become high fatigue very quickly.  While I don't want to make a study of this choosing different ratios of attacker to defender and significantly change the comparison.  The HPS system is very linear.  If you double or halve the unit strengths involved you will still get the same relative results.  Battleground combat is very sensitive to where things fall on the combat tables.