If Spain joined the Franco-Prussian War against France

What if Spain joined Prussia's war against France from the south?

France would lose more heavily, while Spain would probably seek gains in North Africa and might encourage Italy to enter as well.

An additional southern front would make France's military position worse, although the Pyrenees and Basque terrain would constrain Spanish operations. Spain would gain a claim to part of the postwar settlement and could focus on expelling French influence from Morocco and Algeria rather than occupying much of metropolitan France. Italy might also intervene to pursue its own territorial aims once France appeared vulnerable. The scenario therefore widens a continental war into a Mediterranean and colonial redistribution.