Shaka is my neighbour. Bury the hatchet or go for the kill?

After seeing your screenshot, I'll stick with my earlier answer. Fight only if you feel like fighting will be fun. Otherwise, ignore him. You've got Machine Guns, a 60:60 strength ranged unit. He's using 34 strength Rifles that will take a lot of damage if they even dare to attack a Machine Gun.

Your rebuttal will be fully automatic belt-fed death. Assuming he ever gets the stones to try an attack. I bet he won't.

Those machine guns could cause good damage to rifles but if you use infantry and plastics, you could contribute more to your science and eventually get better units that are way better than rifles. Xcom squad could be a good choice here along with a few artilleries to take out rival cities or prevent enemy units from attacking your city.