under what circumstances would it be possible for the Spanish civil war to end in a negotiated peace where the Republicans and the Nationalists control half of the country each? What effects would this have on ww2?
I'm not sure a negotiated peace that kept the country split in two is likely. However, with different results and/or leadership in 1938/1939 you could certainly have a situation where the country is still in a civil war when WW2 starts in Europe in 1939.
If the country is effectively split when WW2 is ongoing, it would likely become an additional front, with both sides sending in more troops/supplies. The Germans could send support to the Nationalists that could divert to take Gibraltor.
under what circumstances would it be possible for the Spanish civil war to end in a negotiated peace where the Republicans and the Nationalists control half of the country each? What effects would this have on ww2?
I think you need Great Power intervention to make this happen. A dictated peace from outside, basically. That being the case, the peace probably does break down once WWII gets going