I ran a poll recently asking this question: "Primarily, I buy Civil War books with a focus on . . ." The three possible answers were: Confederate, Union, or both about equally. Although only 15 people responded, it was about evenly divided (4, 5, and 6, respectively).
The poll did not reflect what sales figures have long told us: Southern/Confederate titles sell substantially better than similar Northern/Union titles--and by a factor of at least 2 to 1.
Let's assume a pair of manuscripts are submitted to us for publication, one on General Smith (CSA), and the other on General Jones (USA). Let's also assume we can only fit one into our program. All things being equal (general's status, writing and research quality, author compatibility with Savas Beatie, etc.), I would select the Confederate-related manuscript. If sales were the sole reason driving my decision, sales history tells me it is the right decision.