Medical science advances with every war. The American Civil War saw surgeons mastering the art of amputation, which saved soldier's lives. Each medical advance meant that more soldiers would survive later wars, though it also meant more would survive with lifelong disabilities. By World War I, doctors could save some men who had their faces blown off, but what about their lives afterward? That called for more medical advances.
The first real plastic surgery was the reconstruction of Walter Yeo's face after he was badly wounded in World War I. Dr. Harold Gillies found Yeo to be a good candidate for a surgical technique he had developed involving skin grafts, but it had never been used for a wounded face covered in scar tissue. It wasn't easy. The technique worked, but Yeo's treatment took years to complete due to infections. We've come a long way since then with, for example, surgical gloves and masks. Gillies improved his grafting technique and was able to repair the faces of many other war veterans with even worse damage. A hundred years later, we've seen quite a few complete face transplants that can restore drastically injured people to a semblance of normal life.