Rhodes focused on national politics. Working from primary sources of newspapers and published memoirs, Rhodes tracked the process by which major national decisions were made. He evaluated the strengths and weaknesses of all the major leaders. He detailed the corruption he found in the [[Reconstruction era of the United States|Reconstruction]] Republican governments in Washington, D.C., and the Southern states. He said that granting of unqualified suffrage to blacks after emancipation was a mistake and added to the problems during Reconstruction.
Rhodes's interpretation of the role of slavery strongly influenced intellectual opinion and historiography. Unlike the first generation of historians, who had been personally deeply committed on the slavery issue, Rhodes approached it dispassionately. He argued that slavery indeed was the main cause of the war. What he meant was an abstract political-economic system that
: The judgment of posterity is made up: it was an unrighteous cause which the South defended by arms; and the tribunal of modern civilization, Calhoun and Davis must be held accountable for the misery which resulted from this appeal to the sword.<ref>Pressly, ''Americans Interpret their Civil War'' p 173.</ref>
By misery he referred to the casualties, deaths, and hardships during the war, not to the miseries of the slaves before the war. He argued it was an irrepressible conflict, that is an inevitable war by December 1860 that perhaps could have been delayed, but would happen sooner or later.<ref>Pressly, ''Americans Interpret their Civil War'' p 173.</ref> For Rhodes, slavery was practically the only cause of the war, and he ridiculed "[[Lost Cause]]" Southerners who justified rebellion as an exercise of the right of revolution in the face of Yankee oppression. He rejected the Calhoun notion of state sovereignty. The issue, he argued, was that the South fought to extend slavery – an institution condemned by ethics, Christianity, and the modern world.<ref>Pressly, ''Americans Interpret their Civil War'' p 172.</ref> Rhodes treated slavery as a calamity for the South, but not a personalized time for white Southerners – he thought they deserved sympathy rather than censure. The South was associated with slavery because of a long chain of events going back centuries. Rhodes downplayed the importance of the abolitionist movement, instead focusing on mainstream leaders such as [[Daniel Webster]] for his promoting a deeper nationalism. Pressley says, "it was Webster's principle of 'Liberty and Union' which won in the Civil War, not Garrison's principle of 'no union with slaveholders.'<ref>Pressly, ''Americans Interpret their Civil War'' p 175.</ref>