Why did soldiers in civil war have so many amputations?

Infections/Tradition: Main reason was(and please correct me other docs if I am wrong), that infections were rampant. Our understanding of germ theory was increasing in those days, but penicillin would not arrive until 1928. With no way to adequately clean or sterilize wounds other than burning, amputation was the only option. Cannon balls were the other cause of lost limbs.

No antibiotics: There were no antibiotics during the civil war to treat infections after a war injury. Also the current standards to prevent spreading infection from one person to the other were not in place so if an infection developed an amputation would be done to save the person.