Riots
The men rioting were enraged by the Civil War draft, especially among immigrants (mostly Famine Irish) who really had no dog in the fight, as well as by the practice of wealthy families paying men from poorer backgrounds to serve in the place of their sons, a kind of bank account driven draft dodge.
In case you had forgotten, it wasn't greater valor that defeated the South, but greater resources. In addition to its greater industrial development and stronger transportation infrastructure, the Union was able to field a larger army precisely because of the draft, and specifically because of the draft of immigrants.