Erik Mathisen's The Loyal Republic is an original contribution to a robust body of studies of loyalty and citizenship during the US Civil War. Building out from the work of scholars such as Stephanie McCurry and Adam I. P. Smith, Mathisen places questions of loyalty at the center of the conflict and its ultimate (if tragic) resolution at the end of Reconstruction. Mathisen portrays loyalty as a plastic cultural, social, and political construct that helped Americans bring order to ruptured local, state, and national sovereignties. His most compelling insight is that in the absence of a clear sense of national citizenship among Americans south or north in 1861, the concept of loyalty assumed an outsized role in determining claims of citizenship, rights, and sovereignty within two rapidly expanding nation-states – the US and the Confederate States of America. In the end, the concept of loyalty tilted toward the aggregation of authority in the nation-state, and led to the cementing of national citizenship in the wake of the war.

Mathisen weaves a compact narrative out of vignettes that demonstrate the waxing and waning of loyalty as a determinant of citizenship during the Civil War era. He highlights the secession crisis and the founding of the Confederacy, the evolution of loyalty (and citizenship) away from a state-centered model, the debate over treason in the Union early in the war, the central role loyalty played in the political thinking of Union leaders such as Andrew Johnson, and the effort by former slaves to construct a new freedom on the foundation of their loyalty to the Union during the war.

Through these examples, Mathisen reveals that both the Confederacy and the Union were forced to construct national citizenship in the fires of war. Redefining loyalty and treason had the practical effect of clarifying who might claim rights of citizenship, who could not, and – vitally – in which government institutions sovereignty resided. In the South, the seceded states soon found untenable their claims either to the loyalty of their citizens or to their own sovereignty. The CSA, growing in strength because of the practical needs of a nation at war, became the de facto repository of southern nationalism as early as 1862. Within the Union, by Mathisen's account, the creation of a national identity took less time. Even before Fort Sumter opened armed conflict in 1861, the actions of secessionists forced northerners to come to grips with the fundamental disloyalty of the slaveholder's rebellion. No doubt existed as to the nature of secession: it was an act against the nation-state, not against coequal states or individuals. Northerners used loyalty to the Union as a means of determining who might enjoy the protection – or feel the wrath – of the federal nation-state. As Mathisen notes, this enabled Unionists to accept the role of power, as opposed to consent, as a legitimate element of nationhood. This shift helped justify the Union's embrace of total war.

Yet loyalty had a short career as the primary factor in establishing citizenship. As Reconstruction wound down, and national citizenship gained wide acceptance, Mathisen notes, loyalty lost its motive force. This had tragic consequences for the freed people of the South, whose wartime contributions to the Union cause had, they believed, provided sufficient evidence of their loyalty to the nation-state to make claims of full rights of citizenship in the aftermath. African Americans’ effort to position themselves unreservedly as citizens of the US entailed the deployment of loyalty as the sine qua non of national citizenship. As Mathisen points out, however, the timing of their claims coincided with the beginning of a rapproachment between North and South that required dispensing of loyalty as a prerequisite for reunification. Though he does not underestimate the role race played in this outcome, Mathisen's larger point is that loyalty as a mark of citizenship was far more critical to the nation-state in war than in reunification. Freed people paid the price.

The Loyal Republic is essential reading for scholars of the Civil War period, providing readers with what might be best described as a political biography of loyalty. Along the way, he offers new insights into key elements of the period. His analysis of the failure of the slaveholder's republic of Mississippi leaves no question that it was little more than a paper government by 1863. No less significant is his argument that the Confederate army, more than any other rebel institution, served as the hothouse for citizenship and loyalty to the nation-state. And his reappraisal of Andrew Johnson persuasively lays out the case that the President's actions during Reconstruction emanated from long-held concepts of loyalty and citizenship, not just personal ambition, racism, and corruption. In these ways and more, The Loyal Republic elegantly combines original interpretation with fresh insights and evidence about the reinvention of American citizenship during the Civil War.