It is rather interesting to note that no less a figure than Raphael Semmes, in his journal entry of Tuesday, September 10, 1861, while commander of the CSS Sumter, and, having been granted an interview with the Brazilian president, states: "I then stated to him that this war was in fact a war as much in behalf of Brazil as of ourselves; that we were fighting the first battle in favor of slavery, and that if we were beaten in the contest, Brazil would be the next one to be assailed by Yankee and English propagandists." This is noted on page 709, series 1, volume 1, of the Official Records of the Navies.
In other words, Semmes himself admits that the war was being fought over the issue of slavery.
Other similar sentiments are echoed later, while he was in command of the CSS Alabama, and while on a visit to a French outpost in the Far East.