This project examined the similarities and differences between the politics of New York City and Philadelphia during the American Civil War. As the war progressed, both cities diverged, with Philadelphia remaining relatively politically stable and politically united throughout, while New York City for much of the war was divided and prone to violence and political extremism. The central question of this project, therefore, was why did Philadelphia and New York City diverge so sharply and if and how did conceptions of loyalty and disloyalty play a role? My project is unique in focusing on how the politics of each city were defined by a conflict over defining loyalty to the Union and the war effort, definitions that evolved as the war progressed. Additionally, it is unique for being the only available work that directly compares New York City and Philadelphia during the war. To conduct this project, I received funding as an undergraduate fellow of the Wolf Humanities Center to access archives in both Philadelphia and New York City. Regarding methodology to accomplish this project specifically, I worked with archivists at the American Philosophical Society, the Historical Society of Pennsylvania, the Kislak Center for Special Collections, Rare Books and Manuscripts at the University of Pennsylvania, the New York Historical Society, the New York Municipal Archives, and the New York Public Library. I also examined digital archives of popular newspapers from both cities, especially those run by leaders of New York City’s intraparty factions like Horace Greeley, Henry Raymond, and Fernando Wood. Finally, I read widely in both general records of each city, as well as in the conduct and history of both cities during the Civil War. Through a mix of these primary and secondary sources, a comparative portrait of New York City and Philadelphia was created that showed where key figures in each city were in agreement and where they were in disagreement. From this methodology, I was able to answer my central question: what separated New York City and Philadelphia was that while the former was driven to violence and political instability by vicious interparty and intraparty feuds, the latter was able to establish a popular, bipartisan consensus. Regarding New York City, I found that its constant political feuding came about because power so easily oscillated between different factions, with voters very easily defecting from one intraparty faction to another. Therefore, there was little to no incentive for Republicans and Democrats to coalesce internally, let alone coalesce on a bipartisan basis. On the other hand, I found that Philadelphia maintained its bipartisan consensus through the shrewd leadership of its wartime mayor, Alexander Henry. Long forgotten (no biography exists on him and he is a insignificant player in the few Civil War works that reference him), Mayor Henry forged a bipartisan coalition called the Peoples Party, later the Union Party. I found, and spend great detail examining, that this coalition evolved throughout the war in its ideological attitudes, starting at its founding in 1857 by feigning no interest in controversial issues like slavery and secession, but eventually endorsing many of President Lincoln’s controversial war aims and practices. Furthermore, I highlighted that a crucial component Mayor Henry used to maintain power was through control of the police, which he deployed both to suppress lawlessness and violence by Union and Confederate sympathizers alike, as well as to include potential dissenting political forces like wealthy Democrats with economic ties to the South in his governing coalition. In the end, after conducting all this research and comparing and contrasting both cities, I was able to conclude that one’s loyalty and disloyalty could not be judged by one’s religion, partisan identification, or even political allies. It especially could not be judged by one’s rhetoric, which was often vague at best and deceitful of one’s true intentions at worst. In fact, if there is one conclusion that this paper easily makes, it is that there were no universally agreed upon, or even mostly agreed upon, definitions of what constituted loyalty and disloyalty, only subjective opinions altered by time and animated by the politics of each city.