Try not to oversimplify how our body works. It's certainly nothing as simple as thermodynamics; it's a series of thousands of different chemical reactions. If all of our food were the same, perhaps that energy balance theory would make sense. But it's not. In fact, our body uses different macronutrients in different ways, mostly due to what your hormone balance looks like.
Please consider reading 'Why We Get Fat' by Gary Taubes.
Hopefully forgotten in a hundred years completely. We make too much of a minor war from back when we were a minor nation. The Civil War is only important to the world because of the end of slavery in the US.