Playing as brazil, I have declared war on venezuela and peru. Venezuela isn't doing much, I've taken one tile but nothing is really happening there. Peru was difficult, I had some initial success pushing in, making Peru very skinny. However, Peru managed to take to push to become HUGE. I then declared war in Bolivia and quickly took most of its territory, but Peru pushed me out. Even with ~100 divisions working together, I can't seem to defeat any of Peru's divisions.
