Although the term PTSD (Post Traumatic Stress Disorder) has only been around for the past 30-40 years, physical and mental changes in soldiers have been obserbed all through out the era of "civilized warfare" and beyond.

Napoleonic Wars and the American Civil War

There is only one possible case of PTSD that I know of during the Napoleonic Wars -and even then it's still highly debatable whether it was actually PTSD- which involves one of France's most well known people from the First Republic, Marshal Michel Ney. His condition most likely started during the disastorous Russian campaign in 1812. It was during their horrid retreat back to France in the brutal Russian winter that Ney began to experience the symptoms. Because honestly, when you see dead frozen bodies and starving horses all around you, you tend to become a bit traumatized to say the least. Some historians believe this influenced his rather rash descision to charge the the enemy cannon at Waterloo. This maneuver proved rather diastorous as well, for the British infantry were formed in anti-cavalry square formations, simply known as squares. As expected, the French cavalry suffered horrendous casualties and failed to break the squares, though it very well might have succeeded if Ney had infantry and artillery supported him.

The American Civil War brought about a revolutionization in the American Medical Department. Lessons were learned that would benefit futher generations of soldiers in future wars, the same goes for PTSD. It was during this war that doctors first began to notice a "change" in soldiers returning home. They were not quite sure what is was, but they seemed different. They eventually discovered that many of the veterans had an increased blood pressure and heart rate. This led to perhaps the first coining of PTSD, which was henceforth known as Soldier's Heart. They called it this because they only obserbed the physical part of the effected soldier (The blood pressure and heart rate), and not the mental part.

It is not to hard to guess why many soldiers were effected. Unlike today's US army, where companies are formed up of men from all of the States, companies back in the civil war all came from the same town or city. It was not uncommon for all the boys in a small town to go down to the recruitment office and all sign up for a single company. Therefore, the soldier beside you might very well be the boy you went to church with every Sunday, or the kid you sat next to in school back in the day, and you might very well be the one to have to tell his mother that he is not coming home.

WWI

World War One brought about a wonderful revolutionization in battlefield tactics and battlefield weaponry. It was during this war that the machine gun, posion gas, the tank, and the airplane were first used. This was also the war where doctors first obserbed the mental part of PTSD, which was now known as Shell Shock. Soldiers suffering from shell shock may have had uncontrollable twitches or muscle spasms, which I am guessing was caused by the action of flinching when an explosion occurs near you. Repeating this over and over again for 4 years could very well have burned the proccess forever in your nervous system. Some soldiers also have been frightened to death if they saw a uniform of the enemy, though this video here best shows you what Shell Shock can do to a person.

https://www.youtube.com/watch?v=RRv56gsqkzs

During WWII, the name was changed to Combat or Battle Fatigue. This was the type of PTSD that many are familiar with, mental breakdowns, outbursts, etc.

It was during the aftermath of Vietnam that we currently have the present term, PTSD. This was also when our knowledge of the condition greatly increased, as we now have a better understanding of how the human brain and anatomy works.