Filling Cartridges at the United States Arsenal at Watertown, Massachusetts, from Harper's Weekly, July 20, 1861

Mass-production techniques pioneered at the United States' armories allowed the Union to fabricate weapons in unprecedented quantities during the Civil War. The yearly production of small arms expanded from thirty thousand at the start of the war to more than seven hundred thousand at its conclusion. It is estimated that 620,000 men died in the Civil War. Firearms cannot be awarded full credit for these casualties---disease and infection were the most efficient killers---but they were the instruments of a military machine that Americans fueled with their hatreds.