The men were also proud of themselves and of their "modern" armies. Nor do they discuss what they are fighting for. They assume that the reader knows already.

IMO reading journals are better than reading history books. The men who wrote the journals were there and were writing, usually at the time, so you can get a good feel for them and their concerns.

They became very hard and robust men. After the first few months in the army the men who were going to sicken and die, sickened and died. The survivors were heathy. They made hard marches in all kinds of weather and they did not give up. They slept on the ground and often, maybe usually, without tents. If it rained their clothes dried on their backs during the march the following day.

They were always hungry, but that is the nature of young me who are on the move.

They went into battle cheering! They sang around the camp fire at night and even to the enemy across the way. When wounded they were quiet so as not to bother the men who were still fighting. The wounded did the best that they could and more than half of them survived, if they got to medical care.

After the war the men on both sides were proud of what they had done, win or lose. Nor does it seem that there was a lasting hatred between the men who had fought. That did not go for the politicians or civilians.

When you look at a football stadium full of fans consider that the mass of people is about as large as the number of union troops deployed at Gettysburg. One section represents the number killed. About 30% of the men involved where either killed, wounded or captured. It was a great mass of humanity!