The sesquicentennial celebration of the Civil War culminates next month with 150-year-old images of City Hall draped in black. “The Nation Mourns,” a banner proclaims from the portico, and thousands of curious and inconsolable New Yorkers queue up to view the body of Abraham Lincoln for the last time.

The miserable war had not been the doing of fanatical agitators, said William H. Seward, the former governor of New York and the secretary of state under Lincoln. Rather, he wrote, “It is an irrepressible conflict, between opposing and enduring forces, and it means that the United States must and will, sooner or later, become either entirely a slaveholding nation, or entirely a free-labor nation.”

In “An Irrepressible Conflict: The Empire State in the Civil War” (Excelsior Editions, State University of New York Press), Robert Weible, Jennifer A. Lemak and Aaron Noble remind New Yorkers that as the historian Harold Holzer writes in his introduction, “No state provided more men, money or matériel for the Union cause.”

This richly illustrated and easily digestible catalog, which accompanied an exhibition of the New York State Museum, makes a strong case for New York’s Civil War primacy, even though Seward, New York’s favorite son, lost the 1860 Republican nomination to Lincoln.