New York was the most populous state in the Union at the start of the Civil War, and, some might say, therefore the most important. It provided tens of thousands of men and women who participated in the war. Many of them held state, city, and national leadership positions, in part because of their abilities and in part because of the power, influence, and money of their state. Most of them were favorably inclined toward preserving the Union, but a few leaders were Copperheads, actively supportin...