Something I’ve always been curious about is how battlefield tactics changed or didn’t change post-napoleonic wars and following the development of guns like the needle gun. Everything I read about wars like the Franco-Prussian war or the Spanish-American war gives in depth analysis to the grand campaign strategies and mentions the battles casualties, where they fought, etc. But I want to understand the tactics behind it. Did they still fight in lines similar to the US civil war? What was the skirmish lines role? How important was flanking and how did they flank? Any help would be a amazing!
By the Franco-Prussian war the close order formations had been abandoned in favour of battalions forming into loose skirmish lines. Here is a picture from the battle of Sedan, taken from the French line. It's a good illustration of how prussian infantry attacked. You can see two clear skirmish lines. Without knowing exactly what we're looking at here I would say that it is a prussian infantry battalion with two companies deployed in skirmish lines advancing and a third company in reserve in column formation on the road.
This was fairly typical. The entire battalion is not comitted at once, rather there are reserves to draw upon as the battles develops which allowed the prussians to reinforce or deploy additional companies as needed. The same area a little later looks like this, the first skirmish line, having advanced fruther, is now falling back. Either because of casualties sustained or because the attack has shifted to the right side of the road (see from the french position). We can see that the rest of the battalion has left the column formation and deployed on the field to the right of the road with a company in skirmish formation in front. The smoke seen in the background is probably prussian artillery firing.
In theory, the french infantry was actually superior to the prussian in terms of equipment and position, particularly here. They have the advantage of longer range, accurate rifles and prepared positions. The prussian on the other hand have the initiative and better artillery support.
I general terms, the Prussians did not win with infantry but with artillery. The prussian steel 6-pounder guns were vastly superior to french artillery in terms of range, accuracy and rate of fire but also in terms of doctrine. The prussian time and again used superior artillery to decimate french gun positions only to the move the guns forward to support the infantry attack.
The prussians also enjoyed a numerical superiority and better concentration of forces thanks to better logistics, mobilization and mobility. This meant that although these pictures show a pretty rough position for the prussians they don't show the whole truth. The effects of prussian artillery on the french positions can not be seen in this picture, nor the fact that the prussians may well have more battalions to the left and right of this supporting the attack.
All this said though, the small unit tactics were not the primary factor behind the prussian victory. Prussian preparations and moderizations and French lack thereof was.