I would be curious to learn of stress caused by intense combat over a short time. I am thinking of Culp's Hill at Gettysburg. Some of the Confederates came under fire at 7 pm on 2 July and remained under intense fire until noon of 3 July with only a few hours of fitful sleep interrupted by sporadic exchanges. The Federals for the most part were taken out of line for short periods, being relieved by fresh or rested troops. The Confederates were also exposed to a frightful artillery barrage at daybreak on 3 July, in addition to heavy gunfire. But they did not break, and even launched assaults in the face of this fire. Companies in both armies came from the same area but I surmise that southern units contained more family members, that seemingly would enhance unit cohesion and keep soldiers at their post. Conversely so many Federal units had large percentages of foreign-born soldiers that would appear to detract from cohesion, unless composed of men all having a similar ethnic background like an all-Irish Catholic command. But the Germans would be different I suppose because Germany was not unified at the time and comprised many diverse states. Simply put, bonds among soldiers in the southern units may have been stronger, at least initially - would this bear upon combat stress? Veterans, on the other hand, were forged under (literal) fire, and their camaraderie strengthened as a result. I'm no combat psychologist, but wonder if knowing your comrades could be counted on to look after you in difficult situations would lift a huge burden that would weigh heavily upon the minds of untried troops.