I have been thinking about this and watching the debates on this board for a good while now. It seems to me that there are two almost antagonistic schools of thinking with respect to what "historical" means in a strategic wargame simulating a whole conflict, like AACW does. Both sides, of course, believe in historical accuracy, but they have drastically different ideas of the meaning of that word.
A) There is that school that believes that a historical conflict simulation is good if
1) with two equally competent players, it produces in most of the cases the historical outcome, i.e. the game lasts as long as historically and is usually won by the side that won it historically; and
2) it has a good chance to follow the historical course of events at least roughly.
This one is the school that advocates with respect to AACW, typically, things like
1) the war should have a good chance to go into 1865 (claiming that a Union victory in 1863 is unhistorical);
2) conscription in the North shouldn't be possible before 1863 (as that was the historical date of its introduction);
3) McClellan should be in charge of the Army of the Potomac (claiming that sending him to guard the Canadian border instead is "gamey").
B) Now on the other hand there is the school that believes that the true mark of historical accuracy in a strategic wargame is the simulation, not the recreation of history. In other words, this school advocates that a historical conflict simulation ought to put the player in the shoes of historical actors by recreating as faithfully as possible the historical conditions that determined their actions, but then give him, within this framework, the greatest possible freedom of action. This school says that the player has a distinct historical role in the game; that for a strategic war simulation like AACW this role is the overall military and political decision-making for the national war effort, i.e. the role historically held by Lincoln and Davis; and that decisions that were historically within the purview of this role should be possible for the player to take. Each decision should have benefits as well as costs, and the player should be forced to make difficult decisions, i.e. weigh for himself whether the benefit is worth the cost. Ideally, he should not be too well aware of either benefits or cost when making his decision, as neither were his historical counterparts.
This school--and as a professional historian I cannot help but feel attached to it, even though I believe it to be in a minority among AACW players (but that's why I made a poll, as I'm curious to find out)--would say that the mere fact that an action was taken historically does in no way mean that it was the only possible, or even the most likely, course that could have been taken. History does not work like that. In fact, history has an odd way of sometimes choosing the most unlikely course and producing the most unbelievable outcomes. Cortés with a few hundred men conquered the Aztec empire, as a result of a most incredible series of accidents. That wasn't preordained, it wasn't even likely. A wargame simulating this encounter would have to go to length to make a Spanish victory even possible and by doing that would distort history to a degree to make playing it not worthwhile. The actual historical outcome is often badly at odds with historical plausibility. Thus a historical simulation, rather than making the unique and often implausible historical outcome of actual conflicts the measure of accuracy, should aim to recreate the generalisable historical conditions within a conflict. In short, it ought to create a sort of historical laboratory in which the conflict, within the framework of its historical conditions, can be run and re-run by players and/or computers to find out the different possible and maybe--if one cares--the most likely outcomes, which will not often be the actual historical ones.
This school--let me call it the "historical conditions school"--would reply to the claims of the "historical accuracy" school roughly as follows, taking the same three points made above as examples:
1) Taking the vast Union superiority in personell, materiel, industry and infrastructure into account, it needed an odd series of comparatively unlikely incidents to let the Confederacy survive (just barely) into 1865. In fact, an unprejudiced observer would find it hard to believe that the Confederacy ever survived 17 September 1862. Anybody, literally anybody but McClellan in charge of the Army of the Potomac at Antietam, and the war would have been over on that very day. Likewise, only sheer luck saved the Confederacy again at Chancellorsville. Both days should have ended with the complete annihilation of the Army of Northern Virginia and brought the Army of the Potomac into Richmond within a fortnight. Only a series of extremely near misses thus saved the South on the battlefield until its luck finally ran out in 1865.
In other words a Union victory in 1863 is not only not unhistorical; but it's the most likely outcome. To make the Confederacy, as a rule, survive into 1865 in a simulation of the Civil War needs to stretch historical plausibility to a certain degree for sure; maybe even to a considerable degree.
2) Conscription was not invented in 1863, nor was it unconstitutional before that year. It was unnecessary, as enough volunteers were forthcoming, and it was rightly considered unpopular. But introducing conscription would have been legally and practically possible right when the war began in 1861. So there is no reason, other than conforming to the historical course of events, why the player should not have that option right from the start. Of course it should come with a hefty morale penalty simulating the likely unpopularity of that decision with the populace as a whole. But leave the player the choice. If he thinks the additional manpower gained by introducing conscription in 1861 is worth say a 30 NM hit, with the attendant combat penalties for his troops, then let him try to put quantity over quality to that extent and live with the results.
3) McClellan really wasn't in any way inevitable. Appointing and dismissing general officers was the commander-in-chief's prerogative in war, if there ever was any. McClellan was no particularly high-ranking, popular or accomplished officer at the start of the war (in fact, he was not even regular army, as he has resigned his commission in 1857) and really became a political figure only when Lincoln chose to drag him from his West Virginia backwater into the limelight. He could quite simply not have done so, and McClellan would never have become the hero of the eastern soldiers and the self-styled saviour of the Republic. Of course, once appointed and popular, McClellan proved harder to get rid of than some other generals, but still, Lincoln could sack him and he did so, twice in fact. And the Republic did not crumble. In short, McClellan was to a large degree Lincoln's own creation, and had he not appointed him, maybe somebody else would have filled that role.
The pertinent point about McClellan is not that Lincoln was forced to appoint him, or unable to fire him--neither is true--but that Lincoln twice found it useful to appoint him. So if the game design finds it worthwhile to induce the player to appoint McClellan, it should not force him to do so, but rather make it attractive for him to do so. Lincoln chose McClellan because he thought--rightly--that McClellan could build an army and--wrongly--that he was a great strategist. So if the game finds it useful to recreate these circumstances, then 1) McClellan's presence should be a palpable boost for coherence and morale of his army and 2) maybe the player should not be quite as aware of the actual performance he can expect of his generals before he appoints them?
But really, in the end, forcing McClellan on the Union player, who otherwise has a comparatively free choice of his army commanders, is putting conformance with individual historical events over historical plausibility. One could as well end up requesting everybody else in charge of the army he led historically. In fact, with this line of thinking one could end up advocating that the Union must not be allowed to invade Georgia before 1864, as it did not do so historically.
Now if the player had the freedom of action in the game that the "historical conditions school" would advocate, what would that mean for the game's competetiveness in PBEM? I suppose with two equally competent players, we would more often see a Union victory in 1863 or so. Would that be so bad? For the historical accuracy school, certainly. For historical plausibility, IMHO, not. For wargaming purposes it would simply need a redefinition of what constitutes a "victory". You could say something like (very simply) if the Union wins by 1864, that's a draw. If it wins in 1863, that's a Federal victory. If the Confederacy makes it into 1865, that's a Reb victory. Or in fact, one could probably leave it to the players to determine (preferably in advance) what "victory" means. Afterall, "winning" or "losing" is not primarily what I am looking for in a historical simulation. I want to re-live the dilemmas faced by the historical actors, be faced with difficult choices, find my own strategies, fight, and keep moving on.

To sum up: Recreating the actual historical course of events in a wargame is in my opinion a rather narrow and superficial understanding of the meaning of "historical". In fact, doing so necessarily needs artifical restrictions of the player's freedom of actions, restrictions by which the historical actors, whose role he takes in the game, were not in any way bound. Therefore, doing so, in my humble opinion, makes the game less historical, and less valuable as a historical simulation.
That having said, I am greatly enjoying AACW, and it is in my opinion the best historical simulation of the Civil War around.

If you made it to here, thanks for reading to the end. Now vote!
