re: On this day 160 years ago, the most savage battle of the Civil War was waged in Virginia

I’m sure you can do an adequate job of explaining the obvious. An industrial society of roughly 22 million people with a standing army in place was able to successfully wear out an agrarian society of 5.5 million that had to raise, train, cloth and provision an army during wartime.
Better prepared, better armed, better supplied, and it took them 4 long years and disproportionate casualties to prevail. Congratulations.