I don't think that the research tree should be limited to Infantry, Tanks, Rockets, Airplanes..basically anything war-related. Instead, it could also have for example, internet, more efficient construction methods, better weapons. The internet would boost country morale by 5. More efficient construction methods would decrease building time by 5%. Better weapons would increase damage by 2%. The point is it shouldn't be limited to warfare, it could also have boosts, boosts that increase productivity and various other things. There should be another branch labelled technology. It would make the research tree an actual research tree.